Major fuel retailers are being urged to cut petrol prices by 5p per litre due to lower wholesale costs.
The RAC, which issued the plea, accused fuel-selling supermarkets of hiking their margins on petrol.
Its analysis found their margins on petrol are around 14p per litre, double the long-term average of 7p.
The latest figures show average petrol prices in the UK are 155.3p per litre.
Petrol prices should be lowered by 5p per litre while diesel should be cut by 4p per litre, according to the RAC.
The 5p per litre cut in fuel duty introduced by the Government in March 2022 “only appears to be helping retailers who have chosen to up their margins”, the company said.
An investigation by the Competition and Markets Authority (CMA) found that supermarket fuel retailers overcharged drivers by 6p per litre in 2022, costing them a total of around £900 million.
The CMA recommended retailers provide live pump price information and a price monitoring body is created.
The Government has pledged to legislate for both those measures.
RAC fuel spokesman Simon Williams said: “Our analysis sadly shows that despite the Competition and Markets Authority’s investigation confirming drivers were being ripped off at the pumps – something we have been saying for years – and the Government acting on the findings, nothing has changed.
“Drivers are still losing out massively when wholesale prices come down.
“But in Northern Ireland, where the supermarkets don’t dominate fuel retailing, drivers are getting fairer deal with a litre of unleaded costing 150p and diesel 157p – 5p less than the UK average.
“Drivers and, indeed, the Treasury, should be furious that the 5p per litre duty cut, which has been in place since the end of March 2022, is not being passed on at forecourts.
“There is no doubt from studying RAC Fuel Watch data that margins are up across the board, and while retailers argue their costs have increased due to inflation, the irony remains that there is a definite link between pump prices and consumer price inflation.
“A failure to cut pump prices to fairer levels when there is a clear opportunity to do so has the effect of keeping inflation artificially high – which is clearly in nobody’s interest.”