The wholesale price of diesel has averaged 4p less per litre than petrol since the middle of last month but this is not being reflected in retail prices, according to a campaign group.
FairFuelUK said despite the difference in wholesale prices between diesel and petrol over the period, the retail price of the two fuels has remained the same, with some outlets selling diesel for a higher price than petrol despite its lower wholesale cost.
Using pricing data sourced from the RAC Foundation and Portland Fuel Pricing it said that the average wholesale price of diesel was 95.29p per litre at the beginning of this month, compared to 96.67p in the middle of March.
The average wholesale price of petrol had increased from 97.58p per litre in the middle of March to 100.16p per litre a the beginning of April.
On average over the period, petrol was 4p per litre more than diesel at wholesale. However, the average retail mark up for petrol was 5p per litre, while for diesel it was 9p.
FairFuelUK said the data showed that retailers were using the lower cost of diesel to hike profits.
Quentin Willson, FairFuelUK campaigner, motoring journalist and broadcaster, said: “Despite plaintive cries of only having a few pence profit per litre, the industry has over the last year been enjoying margins of 10p to 12p a litre on diesel.”
He added: “Many investors are comparing petrol retailing to the cash generation of utility companies, but without the onerous levels of regulation. We think that the extra cost to the UK economy from opportunistic fuel retailing is so significant that it warrants an independent investigation.”
Howard Cox, founder of the FairFuelUK campaign, said: “Retailers are not passing on the benefits of lower oil prices revealed in current wholesale levels and in some cases are now taking a huge 12p per litre in margins. That’s £5 profit from an average motorist each time they fill up.”