Diesel prices at UK forecourts

The price of diesel can differ a good deal from one local area to the next, the Competition and Markets Authority has found. The government now brings together what stations across the UK charge, and the data reaches drivers through apps and websites. With it, drivers can look for cheaper diesel near them before setting off.

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Finding a cheaper forecourt

The service behind this is called Fuel Finder. VE3 Global Limited runs it under the Motor Fuel Price (Open Data) Regulations 2025.

Every motor fuel trader must register with it. Each one also has to report every price change to Fuel Finder inside 30 minutes.

Drivers read the prices on third-party apps and websites that use the data. The government's factsheet notes that some developers are still building it in, and tells drivers to search online for the app or site that works best for them.

The full list can be downloaded as a CSV file, refreshed twice a day. The government says that format is intended for website and app developers.

A pump price that doesn't match

Drivers can tell Fuel Finder when the price charged differs from the one advertised. A report needs the forecourt's name and address or postcode, the date and time, and where the price was seen. Photos or screenshots of the pump, receipt, sign or app can go with it, though nobody has to send them.

A driver can report without leaving contact details. Fuel Finder may share a report with the forecourt operator or local Trading Standards. Where forecourts keep missing the reporting deadline, or keep sending inaccurate data, the CMA can take enforcement action.

Why diesel cost more than petrol for a while

The Competition and Markets Authority (CMA) published the final report of its road fuel market study in July 2023. Up to March 2022, it found, petrol and diesel pump prices had moved in similar ways. After that they drifted apart, and the gap between them stayed much wider from summer 2022 than before.

In the second half of 2022, the CMA's refining spread for diesel (the gap between the crude oil price and the wholesale price) ran well above petrol's. It fell back from late 2022. The retail spread on diesel, and with it the pump price, stayed persistently high.

The CMA estimated that the higher retail margins on diesel added an average of 13p a litre from January to May 2023, compared with margins at their 2017 to 2022 average. Its analysis found the "rocket and feather" pattern in diesel that year. Rises in the wholesale price reached the pump quickly, and falls reached it slowly.

Motorway services

The CMA looked at drivers who fill up at motorway service areas without a fuel card. They make up 20 to 25% of motorway fuel sales. In 2022 their diesel cost them around 15p a litre more, on average, than the same drivers paid away from the motorway.

The CMA saw no evidence that higher retailer costs explained the premium. It put the difference down to limited competition.

The tax in a litre of diesel

Fuel Duty is charged on each litre. HMRC's table puts diesel at the same main rate as unleaded petrol, 52.95p a litre. The rate includes a temporary 5p reduction, which began at the Spring Statement in March 2022.

In Budget 2026, published on 28 October 2026, the government said it would extend the 5p cut for a further six months, to 1 July 2027. It is also deferring the planned increase in line with the Retail Prices Index to the same date.

HMRC lists derv, the road diesel sold at the pump, among the oils that are always standard-rated for VAT. VAT is due on the total value, including the duty.

Red diesel belongs off the road

Red diesel is diesel taxed at a lower, rebated rate. HMRC allows it only in certain vehicles and machines used for particular purposes, which it calls excepted machines.

HMRC's Excise Notice 75 says, "Any vehicle or machine that is not an excepted machine cannot use rebated fuel." HMRC states that it will seize any vehicle using rebated fuel when it is not allowed to, and it can charge a penalty as well.

Petrol in a diesel tank

The AA's first advice to a driver who has filled a diesel car with petrol is not to start it. Anyone who has already started the engine should stop and switch off the ignition as soon as it is safe, then put the car in neutral.

The AA says petrol in a diesel car does more harm than the other way round, because diesel also lubricates the fuel pump system. It warns about AdBlue too, whose small blue filler cap often sits next to the black diesel one. Its advice there is the same: leave the ignition off.

Using less of it

For a diesel engine, the AA suggests changing up at around 2,000 rpm. It says new car models have carried a gear shift indicator since 2014 to help drivers pick the most efficient gear.

The AA also says coasting downhill out of gear no longer saves fuel, because the engine's control unit already cuts fuel to the injectors when the driver lifts off the accelerator.

The petrol side of the same questions, including E10 and E5, is on petrolprice.uk.

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