Diesel car drivers are being overcharged by £9 a tank every time they fill up, the RAC has today warned.
The motoring group explained how diesel remains at least 16p more expensive than it should be, despite falling wholesale costs.
Diesel was 6p a litre cheaper than petrol on the wholesale market at the end of last month.
But the price for a litre of diesel at the pumps cost drivers an average of 159.43p, while petrol was unchanged at 146.5p.
A litre of wholesale diesel cost 104.88p on April 28, down 9p in the month, and unleaded was 111.25p, down 6p.
The RAC believes drivers should really be paying around 143p “at the very most” for a litre of diesel, which would save drivers a staggering £9 a tank.
The driving organisation notes how prices are lower in Northern Ireland, where diesel averages 147.47p.
The latest data from the RAC shows the cost of filling a 55-litre family car with petrol now stands at £80.60, or £87.69 for diesel.
At the end of April, the average price of unleaded at one of the big four supermarkets was 142.99p, which is 3.5p cheaper than the UK average.
Diesel was 2.75p cheaper than the average at 156.68p – down 3p since the start of the month.
RAC fuel spokesman Simon Williams said: "Diesel drivers across the UK mainland continue to lose out badly at the pumps. They’re paying 13p a litre more for the fuel than petrol, despite diesel being cheaper for retailers to buy on the wholesale market for all of April.
"This just isn’t fair for the country’s 12m diesel car drivers. We feel there should be an obligation on retailers to reflect wholesale price movements on their forecourts. "
He added: "Action at a government level is badly needed to stop drivers being ripped off any longer.
"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."
