Supermarkets, oil companies and independent forecourt owners have been accused by the RAC of refusing to lower their retail fuel prices in December, despite a fall in the wholesale price.

The motoring organisation estimates that last month retailers made an average margin of 16p a litre on petrol instead of the normal 6p, and petrol car drivers were overcharged by £5 million a day. Despite wholesale prices meriting big cuts at the pumps, the average price of petrol in the UK fell by just 2p a litre in December. RAC data suggests the price of unleaded should have come down by 12p a litre.

According to the RAC, the price of unleaded petrol fell from 147.47p a litre to £145.48p, when prices should have been closer to 135p for drivers. Diesel dropped by just under 2p a litre from 150.80p to 148.92p when drivers should have been paying around 142p.

“Nothing short of scandalous” is how RAC fuel spokesman Simon Williams described the reluctance of retailers to cut prices.

“In the past when wholesale prices have dropped retailers have always done the right thing – eventually – and reduced their pump prices,” Williams said. “This time they’ve stood strong, taking advantage of all the media talk about ‘higher energy prices’ and banked on the oil price rising again and catching up with their artificially inflated prices, which it has now done.

“Every extra penny they take as margin leads to drivers paying even more as VAT gets added on top at the end of the forecourt transaction. This means the Treasury’s coffers have been substantially boosted on the back of the retailers’ action. We urge ministers to push retailers into doing the right thing for consumers.”

The RAC estimates retailers’ refusal to reflect lower wholesale prices at the pumps cost petrol car drivers £156m in December, or £5m a day.

However, the Petrol Retailers Association has responded by defending its members’ actions. Gordon Balmer, its executive director, said: “December’s pump price data is less reliable because it is taken from fuel card transactions, and there have been far fewer of these transactions because of the reduction in business activity between Christmas and New Year. With pump prices falling towards the end of the month, car drivers travelling over the holiday period are likely to have benefited more than these figures suggest."

“The costs of running petrol stations rose all year, with electricity up 19%, vastly reduced margins from fuel cards, increased national insurance and wage inflation. When volumes fall and operating costs are rising, it makes sense for fuel retailers to raise margins if they are remain in business to serve their customers.”