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Why have diesel prices risen more than petrol prices?



From the start of the American and Israeli war with Iran on 28 February 2026 to mid-September – a period of a little over six months – the retail price of petrol in the UK has risen by approximately 40p, from around 132p to 172p per litre – a rise of 30%. In contrast, the price of diesel has risen by approximately 53p, from around 142p to 195p per litre – a rise of 37%.

In several other countries the percentage difference is greater still, particularly in countries where fuel taxes are lower and thus the wholesale cost of the fuel is a larger percentage of the pump price. In the USA, for example, petrol (gasoline) prices have risen by around 49%, whereas diesel prices have risen by around 71%.

But why have diesel prices risen by more than petrol prices? The answer has to do with demand and supply

Supply

Greater effect of the Iran war on diesel supplies.  The closing of the Strait of Hormuz has drastically cut the supply of oil from the Gulf states. This is being compounded by the Houthi attacks on Saudi shipping in the Red Sea. This has forced Saudi oil that is transported by pipeline to the Red Sea and destined for countries east of Saudi Arabia to be transported north via the Suez canal rather than south through the Bab al-Mandab Strait. This has been made worse by attacks launched from Iraq on the Saudi oil pipeline.

Middle Eastern crude oil’s composition is the most efficient for refining high-quality diesel. The restriction on exports, both of crude oil and of diesel from Gulf refineries, has thus affected diesel supplies more than petrol supplies.

Effect of Ukrainian war.  Ukraine has been launching drone attacks on Russian refineries, mainly producing diesel. The resulting shortage of diesel within Russia has led it to impose a ban on diesel exports, extended at least to the end of 2026, to limit the effects on supplies for the military and for domestic users. Russia has historically been the world’s second-largest diesel exporter, and so this too has had a large effect on world supplies of diesel.

Low diesel stocks.  Stocks of diesel have been run down and this has meant that there is little flexibility to draw them down further.

Refinery constraints.  Refineries cannot instantly alter their output to produce more diesel. Furthermore, diesel has become more expensive to produce in recent years due to the transition to ultra-low sulphur diesel to meet stricter environmental standards. This makes the supply of diesel relatively price inelastic, exaggerating the effect on price.

UK refineries produce more petrol than the domestic market requires, making the UK a net exporter of petrol. This higher self-sufficiency partially shields domestic petrol prices from global shocks. However, the UK does not refine enough diesel to meet domestic demand. It relies heavily on foreign imports to cover the shortfall. Thus diesel prices in the UK are more subject to global price increases.

Demand

Seasonal demand spikes.  The demand for diesel tends to rise in late summer due to extra agricultural demand for autumn crop harvests.

Low price elasticity of demand.  Unlike petrol, which is primarily consumed by individuals who can choose to drive less when prices rise, diesel is essential to industrial economies. It powers lorries, ships, buses, trains, agricultural machinery, mining equipment and many industrial machines. Because businesses must keep moving goods, farming crops and running machines, global demand for diesel is little affected by rising prices. This low price elasticity of demand results in a bigger price rise for every reduction in supply than is the case for petrol.

What is more, the transition to EVs has been greater for cars than for lorries, although many buses and vans are now electric. The electrification of the railways, however, is too long-term a project to affect short-term diesel prices and electric lorries are still in their infancy. But with rapid development of electric alternatives underway in the haulage and industrial machinery sectors, they may become less reliant on diesel in the relatively near future.

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Questions

  1. Draw a demand and supply diagram for diesel and petrol to illustrate the effects discussed in this blog.
  2. Is the demand for diesel likely to be more elastic over the longer term? Explain.
  3. Compare the effects on diesel prices in the UK with one other country of your choice. How similar are the factors affecting the relative price increases in diesel and petrol in the two countries?
  4. Would cutting taxes on diesel solve the problem of higher prices for diesel users?
  5. How has the cost of heating oil and aircraft fuel changed compared to that of petrol and diesel? Explain.
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Feeding Godzilla



The World Meteorological Organization predicts that a ‘super El Niño’ is building. This has been nicknamed ‘Godzilla’. If forecasts are correct, this will be the most extreme El Niño in 1000 years.

El Niño is a natural phenomenon. It occurs when the surface temperatures in the central and eastern tropical Pacific Ocean warm and cause the trade winds that typically blow from east to west across the Pacific Ocean to weaken or even reverse direction. As well as increasing global temperatures and causing intense heatwaves, it can result in droughts in some parts of the world, such as eastern Australia, south-east Asia and southern Africa, and intense rain and flooding in parts of South America, eastern Africa and south-western North America.

Typically, in an El-Niño event, the surface temperature of the central-eastern equatorial Pacific Ocean rises by 1°C to 1.5°C above the average. In the current El Niño, it is forecast to rise by up to 4°C by the end of 2026 and into 2027. It is already between 2.2°C and 2.6°C above the average. The effects could be catastrophic and hence the term ‘Godzilla’.

Although El Niño is a natural phenomenon, its severity is a direct result of climate change. This in turn is a direct result of economic decisions, and the effects will have severe economic consequences.

The economic causes

Climate change is an external cost of private economic decisions. When people or organisations burn fossil fuels, the climate costs of the CO2 emissions are not borne by the emitter. They are an external cost. This is illustrated in the diagram below, which shows the costs and benefits of electricity production from fossil fuels. (Click here for a PowerPoint.)

In this example, to make things simple, we assume that the external climate costs begin with the first unit of electricity generated and increase at a constant rate. The marginal social cost (MSC) of electricity generation equals the marginal private costs (MPC) to the generating company plus the marginal external cost in production MECP.

As you can see, the MSC curve is above the MPC curve. The vertical distance between them is equal to the MECP. It is also assumed that there are no externalities in consumption, which means that the marginal social benefit (MSB) curve is the same as the marginal private benefit (MPB) curve.

Competitive market forces, with producers and consumers responding only to private costs and benefits, will result in a market equilibrium at point a: i.e. where demand equals supply. The market equilibrium price is Ppc, while the market equilibrium quantity is Qpc. At Ppc, with no externalities on the consumption side, MPB is equal to MSB. The market price reflects both the private and social benefits from the last unit consumed. However, the presence of external costs in production means that MSC > MPC.

The socially optimal output would be Q*, where P = MSB = MSC, achieved at the socially optimal price of P*. This is illustrated at point c and clearly shows how external costs of production in a perfectly competitive market result in overproduction: i.e. Qpc > Q*. From society’s point of view, too much electricity is being produced from fossil fuels.

Total social surplus equals consumer surplus plus producer surplus minus the external costs. At the market equilibrium (Qpc) this is areas eaPpc+ Ppcaf – fba (or hjk, as it is the same size). At the socially optimal level of output (Q*) total social surplus is areas ecP* + P*cgf – fcg (or hlm).

Although consumer-plus-producer surplus is higher at the market equilibrium (Qpc) than at the socially optimum output (Q*) by the area cag, the external costs are higher still by the area cbag (or ljkm). Therefore, total social surplus at the market equilibrium is smaller than at the socially optimal point by area abc. This is a deadweight welfare loss and represents the excess of social costs over social benefits at all outputs above Q*. Put another way, moving from Qpc to Q* would represent a gain in social surplus of the area abc, as the fall in external costs outweighs the fall in consumer-plus-producer surplus.

One of the reasons why external environmental costs cause problems in a free-market economy is that no one has legal ownership of the atmosphere. Therefore, nobody has the ability either to prevent or to charge for their use as a ‘dumping ground’ for CO2. Such a ‘market’ is missing. Control must, therefore, be left to the government, international organisations, local authorities or regulators.

But such control is often too little. For example, when President Trump came to office in January 2025, he announced that the USA would withdraw from the UN’s Paris Agreement on climate change and that his policy towards oil production would be to ‘drill, baby, drill’. Indeed, governments globally spend hundreds of billions of dollars a year in subsidising oil, gas and coal production and its use, partly from pressure from the fossil fuel industry and partly to reduce the cost of living for consumers. This embeds fossil fuel dependence.

Game theory can help to explain the slow process of carbon reduction. For an individual country, such as the USA, it might argue that its optimum solution would be for other countries to cut their emissions, while maintaining its own levels. This approach would yield most of the benefits to the USA and none of the costs. However, when all countries argue like this, no progress is made. It’s a prisoners’ dilemma. Only if countries believe that the other countries will (a) ratify an agreement to cut emissions and (b) stick to the approved terms, is the agreement likely to succeed. This requires trust on all sides as well as the ability to monitor the outcomes.

Another major problem area concerns equity. Most countries will feel that they are being asked to do too much and that others are being asked to do too little. High-income countries will want to adopt a grandfathering approach. The starting point with this approach would be current levels of pollution. Every country would then be required to make the same percentage cut. Low-income countries, on the other hand, will want the bulk of the cuts, if not all of them, to be made by the rich countries. After all, the rich countries produce much higher levels of pollutants per capita than do the poor countries, and curbing growth in low-income countries would have a far more serious impact on levels of absolute poverty.

But will a supersized El Niño persuade countries to make deeper cuts in carbon emissions? In recent months commitments to achieving net zero emissions have waned. But the following economic consequences may encourage some countries to make deeper emissions cuts.

Economic consequences of a Godzilla El Niño



Extreme droughts, heat, wildfires and harvest failures in some areas and extreme rainfall and flooding in others will have severe economic consequences, often for the poorest people. There will be reductions in crop yields and loss of livelihood. Food prices will rise globally. This will add to the inflationary pressures from higher oil prices caused by the Iran war.

Droughts and wildfires in south-east Asia and Australia could have disastrous effects on harvests of palm oil, coffee, cocoa, rice, maize, wheat and various tropical fruits. Droughts and heat reduce output from hydropower and possibly wind energy, and industrial production may slow as a result of extreme heat in workplaces.

In Europe, warmer winters and unusually wet springs promote rapid plant growth. When this is followed by summer heatwaves, the undergrowth dries out and provides fuel for the wildfires. A super El Niño will amplify this. France and Spain have experienced massive wildfires these past few months. In the UK, the 2026 summer has been the hottest on record. The costs in Europe of the heat and wildfires in terms of lost crops and animals have been immense.

Floods and storms damage roads, power grids, railways and buildings. This forces governments to spend money on repairs instead of long-term investments. People are displaced and many are likely to lose their lives.

Fortunately, El Niños fade after a few months to be replaced by the cooler La Niña. The problem is that, with global warming, the next El Niño in a few years could be even more extreme with even more serious economic consequences.

The hope is that governments wake up to the pressing need to reduce carbon emissions.

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Questions

  1. What is the current state of progress towards meeting the goals of the UN Paris Climate Agreement?
  2. Are there any externalities in consumption that affect global warming?
  3. How might technological progress make it privately profitable to reduce carbon emissions?
  4. How might global supply chains and shipping be affected by a super El Niño?
  5. What role can education play in tackling climate change and its effects?
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US national debt reaches $40 trillion: but does it matter?



The US national debt hit a milestone in August 2026. It reached a staggering $40 trillion. The national debt is the amount owed by the US federal government to holders of government bonds and bills (treasury securities). The debt grows each year by the size of the annual government deficit, which is the amount that government expenditure exceeds tax and other revenues. The bigger the deficit, the more the national debt grows. The $40 trillion debt represents 126% of GDP – in other words it is more that the total annual output of the USA. It represents around $118,000 per head or $290,000 per household

But does this high and rising debt matter? And how does it compare with other countries?

The comparative size of the national debt

In absolute terms, the US national debt is huge, reflecting, in part, the size of the US economy. In percentage terms (126% of GDP), it is higher than Germany (65%), the UK (104%), Canada (110%) and France (118%) and slightly higher than the G7 average (124%). It is lower, however, than Italy (138%) and much lower than Japan (204%).

What is more, the IMF forecasts that the US national debt will rise from 126% of GDP in 2026 to 139% by 2030. This is because of continuing budget deficits, which require funding. The federal budget deficit is forecast to be around $2 trillion in the financial year ending September 2026 – it was $1.78 trillion in the previous financial year.

Japan’s debt percentage, by contrast, is forecast to fall from 204% in 2026 to 194% by 2030. Also, only about 10% of Japan’s debt is held by foreign investors. Around 90% is financed domestically by Japanese households, local banks, insurance companies, and the Bank of Japan. This makes Japan’s debt more sustainable than the USA’s, where around 28% is held by foreign investors (foreign governments, companies, banks and individuals).

Unlike domestic institutions (such as pension funds), which often have a structural bias to hold domestic assets, foreign investors typically view a country’s bonds as one of many global alternatives and are likely to switch faster to other countries’ assets during periods of market stress. The higher the proportion of bonds held outside the country, the more vulnerable the country is likely to be to bond market speculation.

The UK’s national debt percentage is forecast to fall slightly from 104% of GDP in 2026 to 103% in 2030. However, the UK is a global financial hub and the percentage of debt held by foreign investors (around 30%) is a little higher than in the USA. UK debt held overseas has risen from around 15% in the mid-2000s. It is likely to rise further.

Does high and rising US national debt matter?

Servicing the debt.  In February 2022, the US central bank rate (the Federal Funds rate) was 0.25%. It then rose in increments to combat rising inflation and reached 5.5% by July 2023. Although it has come down slightly since, standing at 3.75% in August 2026, US interest rates are higher now than at any time from 2008 to 2022. With higher interest rates, the USA now pays roughly $1.1 trillion annually just to service the debt. This accounts for around 15% of total federal spending – up from an historical 50-year average of just under 9%.

Upward pressure on domestic borrowing rates.  To fund its deficits, the US Treasury Department must continually issue massive amounts of government bonds. This high volume of government borrowing competes for capital in global financial markets, which can push up broader interest rates. For businesses, this imposes a cost on investment and can act as a disincentive to borrow. For consumers, it adds to cost-of-living pressures by raising the cost of mortgages, car loans, credit card debt and other borrowing.

Crowding out other public spending.  The money spent on servicing the debt is not available for building roads or other infrastructure, funding education, healthcare or defence, or providing social security. Annual interest payments of around $1.1 trillion now exceed national defence spending (around £960 billion), making it the third-largest item in the federal budget after healthcare and social security. As the national deficits and debt expand, so a higher proportion of current taxes is being used to fund past expenditure.

Long-term fiscal risk

The US dollar is the world’s primary reserve currency. This creates persistent global demand for US debt. However, ratings agencies and other organisations, such as the Congressional Budget Office (CBO), warn that adding $1 trillion to national debt roughly every five months is an unsustainable trajectory that could eventually erode confidence in the US economy.

Already, many countries are seeking to expand the range of currencies used as reserves, including Chinese yuan, the euro and crypto currencies. They are also holding more gold. In 2001, the US dollar accounted for 72% of currencies held globally as reserves; by 2025 this had fallen to 57%. This process could accelerate as confidence in the USA is eroded because of the size of the debt and the capricious policies towards trade.

During periods of quantitative easing (QE), central banks, including the Fed, purchased large amounts of government bonds. But now, as central banks scale back their bond holdings in programmes of quantitative tightening (QT), foreign private investors and domestic households are being forced to absorb the majority of newly issued government debt, making pricing and yields increasingly sensitive to global investor demands. A decline in confidence can lead to a large sale of bonds, forcing down their price, thereby forcing up their yield and hence the interest that has to be paid on newly issued bonds. This is what happened in the UK in September 2022 under the short-lived administration of Liz Truss when she and her chancellor, Kwasi Kwarteng, made unfunded promises of tax cuts.

The USA is not immune to such bond market jitters. In mid-August, the yield on 30-year US Treasury bonds reached 5.3% – the highest level since 2007.

A worsening problem

The US deficit is likely to increase, making the national debt rise more rapidly. There are various reasons.

The US population, as in many countries, is ageing and the proportion of retired people is rising. This puts increasing demands on healthcare and social security, with a proportionately smaller workforce to fund them.

The deficit has also been increased by deliberate government policies. For example, Donald Trump’s 2025 ‘One Big Beautiful Bill’ Act made substantial tax cuts, largely for the wealthy.

Congress caps the debt at a certain level and in the past this has acted as a brake on size of the deficit. However, the cap was raised by $5 trillion in 2025 and this could well happen again, allowing debt levels to expand further.

But reining in the deficit could have a contractionary effect on the economy as taxes are raised and/or expenditure is cut. Governments are reluctant to do this as it could lead to recession, or at least falling growth in the short term, and this could affect their chances or re-election. With the mid-terms approaching in the USA, and the presidential election just two years later, this is an unlikely policy for the Trump administration to pursue.

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Questions

  1. Distinguish between national debt, central government debt and general government debt.
  2. Would it be possible to run a budget deficit and yet for the national debt to fall as a percentage of GDP?
  3. Japan and Italy have a higher debt to GDP ratio than the USA or the UK. Why are they less subject to bond market pressures than the USA or the UK?
  4. What policy measures would you recommend to the US government to tackle the rising national debt and why?
  5. Could the USA ‘grow its way out of the debt problem’?
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Propping up the yen?



The yen has been depreciating against the dollar and other currencies for several months. It fell from 100 yen = $0.97 in January 2021 to $0.61 by the end of July 2026 – a fall of 37%. This marked a 40-year low. But then, at the end of July it rallied and by 3 August the rate was 100 yen = $0.64 – a rise of nearly 5%. But why did this happen and what will be the implications for Japan and the wider world economy?

Why has the yen fallen so much since 2021?

There have been two main drivers.

The first is fiscal policy. For many years, Japan has been pursuing expansionary fiscal policy in an attempt to stimulate the sluggish economy. This has led to large budget deficits and public-sector debt. Since 2020, general government gross debt has been around 255% of GDP, the largest of any high-income economy.

Recently, the Japanese government has adopted aggressive supplementary budgets to fund, among other things, fuel subsidies and public-private investment initiatives. This has involved the issuance of more government bonds to fund the necessary borrowing.

Fiscal pressures have also increased becase of demography. A rapidly aging population and declining birth rates have required substantial public spending on healthcare, social security and pensions. Meanwhile, the tax-paying working-age population has declined as a proportion of total population.

On the plus side, unlike most highly indebted nations, over 90% of Japan’s debt is held domestically by Japanese residents, Japanese institutional investors, banks and the Bank of Japan (BoJ). This lowers the risk of default and hence the risk premium on Japanese bonds.

The second driver is monetary policy. Interest rates have been kept low over many years, including periods of negative rates, as the BoJ has attempted to stimulate the economy. Low interest rates have sometimes been backed up with quantitative easing to increase money supply.

Since March 2024, however, there have been four interest rate increases. The latest was in June 2026 when the BoJ raised the short-term policy rate from 0.75% to 1.0% – the highest level since 1995. Despite this, interest rates have remained below those in other countries, and this contributed to the continuing fall of the yen.

A falling yen has helped to increase Japanese exports by making them more competitive, but more expensive imports have contributed to rising Japanese inflation.

Low interest rates have also stimulated the yen-dollar carry trade. This is where investors borrow money in yen at low interest rates, convert it into US dollars and invest it in higher-yielding US assets, typically US government bonds (‘Treasury bonds’). This borrowing in yen to buy dollars further contributed to the depreciation of the yen against the dollar.

Co-ordinated intervention

In an attempt to raise the value of the yen, the Bank of Japan and the US Federal Reserve acted together – their first joint currency rescue operation since 2011. The BoJ spent tens of billions of dollars to buy yen; the US Treasury bought yen by selling euros. Prior to the intervention, global hedge funds held near-record short positions against the yen, meaning that they sold yen at a current price, agreeing to buy them back at a particular later date, hoping that the yen would fall in the meantime and that they would therefore make a profit. The sudden joint intervention forced these traders to buy back the yen to cut their losses before the rate rose further. This accelerated the yen’s appreciation.

But why did the USA join Japan in intervening? Japan is the largest foreign holder of US Treasuries ($1.1 trillion). The USA intervened to discourage Japanese investors from selling US Treasuries in order to raise cash, thereby pushing up US borrowing costs.

The rise in the yen was also encouraged by speculators who are expecting further interest rate rises from the BoJ to counter inflation and support public finances, driving domestic bond yields higher. This will lead to a narrowing of interest rates between Japan and other countries.

Effects on the Japanese economy

If the yen continues to appreciate, this will help to reduce inflation by making imports cheaper and will help to ease cost-of-living pressures on Japanese consumers. Japan is heavily reliant on imported energy and raw materials.

However, the decline in the yen over recent years has provided a large boost to Japanese exports. A sharp reversal in this could severely affect exporters’ profits and have a serious negative impact on economic growth.

If the appreciation continues, it would lead to an unwinding of the carry trade. To prevent mounting currency losses, highly leveraged institutional investors would be forced to sell assets, such as US and other countries’ shares and bonds to buy back yen and pay off their debts. This potentially massive unwinding would be likely to create global market volatility and drive up interest rates.

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Questions

  1. What have been the benefits and costs to Japan of a depreciating exchange rate?
  2. Explain the carry trade.
  3. Why might the yen-dollar carry trade unwind and what would be the consequences for Japan and the USA?
  4. Find out what has happened to the exchange rate between the yen and the euro. Has this been driven by the carry trade?
  5. For what reasons might the yen (a) now continue rising; (b) resume depreciating?
  6. Find out what has happened to the yen/dollar exchange rate since this blog was written. Explain your findings.
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Holy Mackerel! Soaring fish prices


The prices of many species of fish have risen in recent months. Coastal pelagic fish, such as mackerel, herring and sardines have risen especially rapidly. Mackerel, once seen as a cheap source of protein, is no longer quite such a ‘bargain’.

From January 2023 to May 2026, the international price index of pelagic fish rose by 69%. In 2025, UK supermarket fresh, chilled smoked and tinned mackerel prices rose by an average of 25%; and over the first part of 2026, some tinned mackerel product lines have increased by as much 55%. In February 2026, Waitrose announced that it would suspend sales of fresh and chilled mackerel and tinned mackerel once current stocks had been cleared. It cited overfishing and sustainability concerns.

Supply and demand

But why have mackerel prices risen so much? The price of fish is determined by demand and supply. So what has changed? The main changes have been on the supply side.

Supply.  Most of the world’s supply of mackerel comes from the Northeast Atlantic. These waters have been overfished for many years, thereby depleting the stock of the fish and reducing the amount of mackerel caught.

To arrest the decline and allow stocks to rebuild, the International Council for the Exploration of the Sea (ICES) recommended a quota of 174,357 tonnes for 2026. This would represent a 70% cut from 2025. The main fishing countries – Norway, the UK, the Faroe Islands and Iceland – eventually agreed to a quota of 299,010 tonnes: a cut of 48%. After a series of bilateral agreements between the four countries over access to each other’s waters, this resulted in the following quota shares: UK 30.55%, Norway 26.4%, Faroes 12% and Iceland 10.5%. The remaining 20.55% would be for the EU, Greenland and Russia.

Despite these other countries not being part of the deal, in May 2026 the EU agreed to reduce its catch by 48% too. Russia, however, set its own quota of 67,548 tonnes, which is 22.6% of the total 299,010 quota, above the 20.55% set aside for the EU, Russia and Greenland combined and almost almost five times Russia’s historic quota share! The UK, EU and Iceland responded by agreeing to bar Russian vessels carrying mackerel from entering their ports.

The quotas have added to the decline in supply, even though the aim is to increase supply in the future as stocks are rebuilt. In May this year, the Norwegian catch was down nearly 85% – well below the 48% reduction in the quota.

Demand.  Despite higher prices, demand has remained strong. Part of the reason is that demand is relatively inelastic. This is because, despite its increase in price, mackerel remains a relatively cheap fish and thus there is little option to switch to cheaper alternative fish. Indeed, with other fish going up in price, and meat too, some people may even switch to mackerel.

Another reason for strong demand is the growing market outside Europe, especially in southeast Asia, China, South Korea and Japan. In some of these countries, mackerel is seen as a luxury fish and people are prepared to pay higher prices, making demand relatively inelastic but at the other end of the market. In 2025, imports of frozen whole mackerel into the region rose by nearly 9%, despite rising prices.

However, Norwegian exports to the region have been falling, reflecting lower quotas in 2025 and lower still in 2026. This has further exacerbated the rise in price and intensified competition between Asian importers. For example, in July 2026, Korea sent a ‘mackerel envoy’ to Norway and other major exporters to seek to secure additional supplies.

The future

With supply restricted by declining stocks and tighter quotas, and with a price inelastic and growing demand, the high prices of mackerel in all forms look set to last – at least until stocks rebuild and quotas can be relaxed. But, with total quotas well above the level suggested by the ICES, rebuilding could take a long time.

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    • European Market Observatory for Fisheries and Aquaculture Products (EUMOFA)

Questions

  1. Draw a supply and demand diagram to illustrate what has happened to mackerel prices.
  2. What is the effective price elasticity of supply of mackerel?
  3. Why is demand for mackerel relatively price inelastic in the UK, except when prices rise above a certain level?
  4. Why is demand for mackerel relatively price inelastic in certain Asian countries, such as Japan and South Korea?
  5. In which country is demand for mackerel likely to be more income elastic: the UK or Japan?
  6. Under what circumstances might the price of mackerel in five years’ time be (a) higher than now; (b) lower than now? What will determine which is more likely?
  7. Should other supermarkets follow Waitrose’s lead in stopping the sale of mackerel?
  8. What is the ‘tragedy of the commons’? Why is a common resource such as fish in the open seas likely to result in the tragedy?