Fuel prices fell 9p a litre in December, but the RAC believes the decreases do not reflect much lower wholesale prices.
Its Fuel Watch data found that petrol prices fell by 8.4p last month while diesel came down by 9.4p.
However, with wholesale prices down considerably since mid-October, the RAC believes petrol should be as much as 11p less than the current UK average while diesel prices should be 14p lower than the average at the end of 2022.
RAC fuel spokesman Simon Williams said: “On the face of it, December looks like it was a good month for drivers with 9p coming off at the pumps on top of November’s 6p, but there’s no question that the drop should have been far bigger given how far wholesale prices have come down.
“For weeks we’ve been calling on the big four supermarkets to cut their prices more substantially to give drivers a fairer deal when they fill up, so even though they have reduced their prices collectively by more than 10p a litre in December, they are still nowhere near where they should be given the scale of the drop in wholesale prices.”
He added: “In Europe prices are considerably cheaper as the average price of a litre of unleaded is 144p and diesel 152p. And just across the Channel in France unleaded is an average of 146p and diesel 154p. In fact, when compared to the 27 EU countries we currently have the second most expensive diesel and the sixth most expensive petrol.”
