The major supermarkets have been blamed by the RAC as it claimed fuel retailers did not pass on full savings to motorists after the wholesale prices of petrol and diesel fell during August.

According to RAC Fuel Watch, the average price of a litre of petrol reduced 0.27p to 128.88ppl during the month, but the wholesale price came down by 4.38p to 96.57ppl. Meanwhile, the pump price of a litre of diesel decreased by 0.38p to 131.66p while its wholesale price fell by 1ppl to 101.12ppl.

The average price for petrol at the country’s four biggest fuel retailers – Asda, Tesco, Sainsbury’s and Morrisons – was 125.41ppl (a reduction of 0.55p) and 128.04ppl diesel (0.6p saving on July). At the end of August Asda recorded the lowest prices for both petrol and diesel at 124.08ppl and 126.05ppl respectively.

RAC fuel spokesman Simon Williams said: “Drivers have the right to feel angry that the price of fuel did not fall more in August than it did. With nearly 4.5ppl coming off the wholesale price of petrol drivers should have seen, at the very least, 2ppl being knocked off at the pumps by the end of the month.

“While the average price charged by the supermarkets came down a little more than the UK average they should really have led the way with larger cuts which would have spurred other retailers to reduce their prices too.

“By our calculations retailers ought to be charging around 126p for a litre of unleaded based on a wholesale price of 98p a litre, which many retailers will have bought at a couple of weeks ago, and then factoring in delivery, a reasonable margin of 5p a litre and VAT. As for the supermarkets they could easily be selling at around 122ppl.

“If you look at the average cost of fuel in Northern Ireland you can see this is possible as the average price of petrol there is 126.01ppl and diesel is also more than 2.5ppl cheaper at 129.02ppl. If Northern Ireland can charge a fairer price why can’t retailers in the rest of the UK do it. For this reason we strongly urge all retailers outside of Northern Ireland to cut their prices in the next week by at least 2ppl on both petrol and diesel.

“There was a time when a 4.5ppl reduction in the wholesale price would have led the supermarkets to cut their prices significantly, but unfortunately those days seem to have passed as they no longer appear to have the appetite for them despite the clear wholesale market dip. Perhaps they are hedging their bets thinking there could be a further drop in the value of sterling which will could cause wholesale prices to increase again.”