International Energy Agency rules say member states, including the UK, must hold oil stocks equivalent to 90 days of net oil imports.

EU rules say member must hold reserves to cover 61 days of domestic consumption. In total the EU holds nearly 109 million tons of emergency crude and fuel stocks, with around a third in diesel and related fuel products.

A European Commission spokesperson said that there were “lots of calls, lots of meetings” taking place on the diesel situation, including with “high level contacts” in the US administration.

Potentially adding to the pressure on the global diesel market, Chinese refiners have reportedly halted October exports of some fuel products as Beijing prioritises domestic supplies.

Prices of petrol and diesel globally have skyrocketed since the outbreak of the US-Israel war in Iran in February. The closure of the vital Strait of Hormuz, which typically transports around a fifth of the world’s oil and gas, has pushed up the price of products made from oil.

An export ban from Russia, also a major supplier of diesel, has added to the pressure on prices.

Trump has argued that keeping any surplus barrels of diesel in the US would lower pump prices domestically, offering immediate relief to drivers, truckers, and businesses ahead of the midterm elections.

But David Fyfe, chief economist at Argus Media, said cutting off American supply would be likely to cause international prices to skyrocket.

Diesel prices have hit an all-time high in the UK, with the latest RAC figures showing average pump prices at 199.79p per litre, up from 142.38p

Diesel is harder to refine than gasoline and, because it is used by the haulage industry and in agriculture, it is very difficult to reduce demand.

The UK is heavily reliant on imports. Although the four refineries in the UK make more than enough petrol to meet demand, they do not make enough diesel for the country’s needs.

There were 15.1 million diesel vehicles on UK roads at the end of June, according to the Department for Transport. That is a drop from 15.7 million a year before.

There were 9.8 million diesel cars, down year on year from 10.4 million.