Drivers of diesel vehicles are paying 20p per litre more for diesel than petrol, despite a wholesale cost difference of just 6p.

RAC Fuel Watch data shows the average price of diesel was 168p per litre, last week, while the wholesale cost was 121.06p. It means retailers are pocketing more than double the margin on every litre they sell, compared to petrol.

The RAC calculates that if diesel was being sold at a fairer rate drivers would be paying no more than around 155p per litre, which would make the cost of filling an average 55-litre family car £7 less than it is today (£85.25, compared to the current £92.40).

RAC fuel spokesman Simon Williams said: “For nearly a month, the gap between wholesale petrol and diesel prices has been less than 10p a litre and in recent days it has reduced to just 3.5p, yet average diesel prices at the pumps remain stubbornly high having fallen by only 2p since the start of February.

“Membership-only retailer Costco has been able to cut the average price of a litre of diesel by a massive 4p this week shows what’s possible, but we badly need other fuel retailers to treat drivers of diesel vehicles fairly.

“Even though the price of diesel is not being cut as quickly as it should be, the gap between the average prices of petrol and diesel has dropped to under 20p (19.99p) for the first time since 10 October 2022. If retailers now do the right thing this should reduce significantly, saving drivers who rely on diesel a lot of money every time they fill up.”

The RAC is calling on retailers to urgently cut the price of diesel to fairer levels, following the lead of membership-only retailer Costco which this week lopped 4p off diesel at its sites across the UK, meaning it is now charging an average of 154.7p – 13p less than the UK average and 11.5p less than the average at the UK’s big four supermarkets.