The RAC reports that the price of diesel fuel fell by nearly 4p a litre in April, yet retailers have not passed these savings on to drivers.

It said diesel is now 6p cheaper than petrol on the wholesale market, and a litre cost 104.88p on April 28, a 9p fall over the month. In comparison a litre of unleaded petrol was 111.25p, a decline of 6p in April.

Yet a litre of diesel is currently 159.43p at UK forecourts, compared to 146.5p for petrol.

Diesel costs have been falling for six months

The price of diesel has dropped for the past six months but drivers lose out when the wholesale reductions aren’t reflected  in the price at the pump, the RCA said.

It said diesel was still 13p more expensive per litre on average than petrol, except in Northern Ireland.

If prices were filtered through, the RAC said drivers should be paying around 143p at the very most for a litre of diesel. If this were the case, it would typically save drivers £9 every time they filled their tank (it costs an average of £87.69 to fill a 55-litre family car compared to £80.60 for petrol).

At the end of April, a litre of petrol cost an average of 142.99p at one of the big four supermarkets, 3.5p less than the UK average. Diesel from those stores was 156.68p per litre, 2.75p cheaper than the UK average.

‘Diesel drivers continue to lose out’

Simon Williams, RAC fuel spokesman, said: “Diesel drivers across the UK mainland continue to lose out badly at the pumps.

“Our data shows that the average retailer margin on a litre of diesel is a shocking 22p a litre compared to petrol which is around 8p. The long-term averages for both fuels is 7p which means retailers are making three times what they have in the past for diesel. This is hard for them to justify and equally hard for diesel drivers to swallow.

He said that action at a government level was needed “to stop drivers being ripped off any longer.”

Williams continued: “While we’re not in favour of prices being capped – as we feel this could lead to smaller retailers in rural areas not being able to compete and going out of business to the detriment of the communities they serve – we feel there should be an obligation on the biggest retailers to charge fairer prices in relation to wholesale market movements.”