Fuel retailers have been slammed for a “shocking” gap of more than 17p between petrol and diesel prices at forecourts after wholesale costs hit parity.

Diesel is still being sold for 17.5p a litre more on average at forecourts across the UK despite wholesale cost parity with petrol

Data from RAC Fuel Watch reveals that pricing for the two fuels is now virtually identical on a wholesale level, at some 114.5p. But the average price of petrol stands at 146.63p while diesel is 164.26p.

It means retailers have taken a margin of nearly 20p per litre of diesel on average throughout March, compared to the long-term average of 7p, proving devastating for every driver and business that relies on diesel.

RAC fuel spokesman Simon Williams said the price of a litre of diesel at forecourts should have already come down to around 152p and the latest fall in wholesale costs should have brought it down further to 147p.

He added: “Sadly, this seems unlikely given current retailer behaviour. Instead, the big four supermarkets, which dominate UK fuel retailing, are charging an outrageous of 162p a litre on average.

“As the supermarkets buy so frequently, they have had plenty of time to pass on the lower prices they are benefiting from on the wholesale market to drivers at the pumps, but they remain totally resolute in their refusal to cut their prices substantially which is nothing short of scandalous, particularly in a cost-of-living crisis. The sole national retailer prepared to buck this trend appears to be membership-only chain Costco, which is charging just under 150p a litre for diesel at the moment.”

Many independent retailers are also charging far less than their supermarket rivals – which the RAC said was a sign of how much fuel retailing has changed.

“This would have been pretty unusual several years ago but is now rapidly becoming the norm. If smaller retailers can afford to make ends meet with lower margins and smaller sales volumes, then what excuse can the supermarkets possibly have for keeping their diesel prices so high?” Williams pointed out.

He also called for the Competition and Markets Authority, which is currently reviewing the road fuel market in the UK, to note the pricing behaviour.

Emerging analysis published late 2022 from the probe by the UK’s competition watchdog has already found evidence of  ‘rocket and feather’ pricing on road fuel last year – particularly for diesel. A letter from the then Business Secretary Grant Shapps last December urged retailers “to take any steps necessary to ensure savings are passed on to consumers” and warned that the Government would “not hesitate to act to ensure competition is healthy and consumers get a fair deal on their fuel”.