Big supermarkets have been accused of refusing to pass on fuel savings to British drivers, despite the recent fall in the oil price.
New data from the Department for Business, Energy and Industrial Strategy showed that a litre of petrol now costs an average of 165.5p, while diesel was 181.1p per litre.
But the RAC claims that petrol should really be priced at 153p a litre and diesel at 175p.
It has accused Tesco, Sainsbury's, Asda and Morrisons of failing to pass on savings to consumers following the slump in the price of crude.
Simon Williams, RAC fuel spokesman, told the Telegraph: "Prices should have fallen much further than they have due to the big reduction in the cost of wholesale fuel this summer.
"And the main reason this hasn't happened is that the big four supermarkets, which dominate UK fuel sales, have refused to pass on savings they are benefiting from by buying cheaper wholesale petrol and diesel."
Margins much higher
Retail fuel margins are now 19p a litre, said Mr Williams - 12p more than the long-term average.
"Petrol should really be on sale for 153p a litre and diesel 175p," he said.
Mr Williams said independent retailers, which have traditionally been far more expensive than their supermarket rivals, are now often selling at lower prices.
Larger retailers tend to buy their petrol further in advance, meaning changes to wholesale prices are slightly slower to filter through to consumers, according to an industry source.
Andrew Opie, of the British Retail Consortium, said: "Retailers understand the cost pressures facing motorists and will do everything they can to offer the best value-for-money across their forecourts, passing on cost reductions as they feed through the supply chain."
A spokesman for Asda said: "Asda has consistently offered motorists the best value at the pumps. Since the start of July, our prices have fallen by 25p per litre on petrol and 18p per litre on diesel. In addition, today's prices are 2p per litre below the UK average on petrol and 3p per litre on diesel."
Name and shame
Earlier this year, former prime minister Boris Johnson declared war on petrol stations that fail to pass on the Government's fuel-duty cut, pledging to name and shame those that refuse to drop their prices.
Mr Johnson expressed fury that the 5p-a-litre cut to fuel duty announced in March was failing to pass through to prices at the pump, prompting an investigation by the competition regulator.
In July, the Competition and Markets Authority launched an investigative study into the relationship between wholesale and retail prices, which is due to be published in the autumn.
The Telegraph says the highest average fuel prices for the year so far were recorded on July 4, when petrol was 191.6p per litre and diesel nearly hit 200p per litre.
Since then, the cost of filling up a typical 55-litre family petrol car has been cut by more than £14, while refuelling diesel models costs nearly £10 less.