If retailers passed on oil price cuts to consumers, petrol would cost 8p less per litre.
The average litre of petrol is still around 8p per litre too expensive, despite fuel prices falling in December.
That’s the conclusion drawn by the RAC, which monitors fuel prices on a monthly basis.
According to the organisation, the average litre of unleaded petrol in the UK cost 120.92p at the end of December - a 2.75p reduction on the price at the start of the month.
However, oil prices have been falling over the past few months, and the RAC says fuel retailers have not passed those savings on to consumers.
Were motorists to feel the full force of the oil price cuts seen in December, the motoring organisation says petrol should cost around 113p per litre within the next two weeks - a reduction of around 8p.
And the organisation says drivers of diesel-powered cars are even more out of pocket, with prices standing around 10p per litre higher than they should.
At present, the average litre of diesel costs 130.01p, which represents a saving of 3p per litre on the prices at the start of December, but the RAC says that current oil prices should see diesel sink to around 120p per litre.
RAC fuel spokesperson Simon Williams said supermarket fuel retailers were partly to blame, with only Asda choosing to cut its prices as the oil price tumbles - and then only by a small amount.
“While it’s good news fuel prices have fallen for the second month in a row, drivers should feel cheated they have not come down further,” he said.
“The decision by all supermarkets to take more profit on a litre has led to every driver having to pay more to fill up than they should have to. This is because the UK average is negatively affected as other retailers are not being forced through competition to lower their prices.”
According to Williams, this change in the fuel pricing landscape could have worrying consequences, with drivers being forced to pay over the odds for fuel.
“If this new pricing behaviour continues into 2019 this could spell a bleaker year for drivers at the pumps no matter what happens to the price of wholesale fuel,” he said. “Drivers could be paying around 3p a litre more for their fuel simply because of a retail pricing decision at three supermarkets which together sell a high volume of fuel. This is important as supermarkets only operate 18 percent of the UK’s 8,422 forecourts, but sell around 45 percent of all the fuel.
“Of course, it should also be the case that smaller retailers ought to be moving their prices down on their own without having to be forced to do so by nearby supermarkets. We commend those smaller retailers that proactively do this.”