Diesel drivers are being “ripped-off” at the pumps to the tune of around 16p per litre, according to a motoring group.

The RAC, along with others, has long argued that British motorists and businesses are paying over the odds for the fuel – the engine behind the UK economy – fanning the flames of inflation and the cost of living crisis in the process.

RAC Fuel Watch analysis showed diesel was 6p a litre cheaper than petrol on the wholesale market at the end of last month.

The average pump price, however, stood at 159.43p while petrol was unchanged at 146.5p.

While the report noted a 4p-per-litre drop for diesel at forecourts during April it said prices in Northern Ireland, where there is a fuel price transparency mechanism in place, were more realistic at 147.47p.

It believed drivers should be paying around 143p “at the very most” for a litre of diesel.

UK drivers faced record fuel bills last year when Russia’s war in Ukraine drove up the cost of oil.

Fuel became a major driver of inflation, which hit a 41-year high last autumn.

Costs have only slowly eased as oil prices have come down from their June 2022 peak and supermarkets, which used to lead the way on fuel price cuts, signalled last year that the days of cheap fuel were over as they concentrate their firepower on food value due to the squeeze on household budgets.

However, fuel promotions are once more being used by stores as lures for shoppers.

The RAC said supermarket diesel was 2.75p cheaper than the national average price while the figure stood at 3.5p for unleaded.

Motoring groups and campaign groups have long argued for greater transparency over the price of petrol but a Competition and Markets Authority report last year essentially gave retailers a clean bill of health.

RAC fuel spokesman Simon Williams said: “We feel there should be an obligation on retailers to reflect wholesale price movements on their forecourts.

“Sadly, the only place this seems to happen is in Northern Ireland where a litre of diesel is, incredibly, being sold for 12p less than the UK-wide average.

“Our data shows that the average retailer margin on a litre of diesel is a shocking 22p a litre compared to petrol which is around 8p.

“The long-term averages for both fuels is 7p which means retailers are making three times what they have in the past for diesel. This is hard for them to justify and equally hard for diesel drivers to swallow.

“Action at a government level is badly needed to stop drivers being ripped off any longer.”

Gordon Balmer, executive director of the Petrol Retailers Association which represents independent operators, responded: “The independent sector accounts for approximately 36% market share by fuel sale while the supermarkets are market leaders at 45%.

“Due to their market share, supermarkets are price leaders and in many cases our members will use them as markers for pump prices when operating in the same area.

“This dynamic is now shifting, with many commentators noting that independent forecourts are increasingly offering more competitive prices.”

A spokesperson for the British Retail Consortium, which represents the major retailers, told Sky News: “The price of diesel has been falling consistently throughout 2023 as retailers aim to provide their customers with the best value for money.”