Only 10% of filling stations are charging drivers a fair price for fuel, with independent forecourts leading the way, according to the RAC.
Wholesale fuel costs have fallen substantially over the last six weeks but the motoring organisation says only a tiny proportion of retailers have cut their prices to accurately reflect this.
It has urged filling stations to “do the right thing” and bring respite to drivers struggling with the current cost of living crisis.
Based on the latest wholesale fuel prices, the RAC estimates a “fair” price for petrol is 174p per litre, while diesel should be around 189p per litre. That factors in the wholesale cost to retailers, a 7p per litre margin and VAT.
On average, a litre of petrol is currently around 187p per litre and diesel close to 196p, according to analysts Experian Catalist.
Based on the RAC’s survey of 4,500 filling stations, only 157 are charging between 170.9p and 179.9p for petrol while 250 are charging less than 189.9p for diesel.
The other 90% are charging more than 180p for petrol and almost 1,000 are charging in excess of 190p for unleaded.
Supermarkets have traditionally been the best-value filling stations but the RAC study found independent forecourts are currently leading the way.
Of the 157 selling petrol at less than 180p, 125 are independents, 28 are major supermarket sites and four are owned by oil companies. Similarly, 192 of those selling diesel at less than 190p are independently owned with just 43 being run by major supermarkets and 15 being owned by oil companies.
RAC fuel spokesman Simon Williams said: “In this most expensive of summers, drivers need all the help they can get to keep their spending down so we applaud those retailers who are doing the right thing for their customers and charging a fair price for petrol and diesel, more in line with the lower wholesale costs.
“Weekly wholesale petrol prices – that’s the price retailers pay to buy the fuel – have fallen by a massive 17p a litre, from a weekly average of around 152p at the start of June to just 135p. Yet average pump prices have reduced by a paltry 4p. It’s time for every retailer to do the right thing and cut their prices to more reasonable levels.”
Mr Williams said the latest data showed the days of the supermarket petrol prices wars were over, as the big chains focused on grocery prices instead, adding: “Drivers who fill up at supermarket forecourts have every right to feel let down that they are being charged well over the odds for petrol and diesel right now."
Earlier this month, the AA estimated that petrol could fall by as much as 20p per litre if retailers chose to pass the full wholesale price drop on to motorists. Its fuel spokesperson, Luke Bosdet, said that could cut up to £10 off the cost of a tank but warned that “price cuts are quite simply not happening”.