Fuel retailers have been accused of using the “distraction” of the general election to keep petrol and diesel prices “persistently high”.
The RAC said the cost of filling up at the pumps was “far higher” than would normally be expected as wholesale costs had fallen since the end of April.
The average price of a litre of petrol across the UK is currently 146.3p, which is “5p more expensive than it should be”, according to the motoring firm.
It said the average price for the same product was 141.1p in Northern Ireland.
Meanwhile, a litre of diesel in the UK costs an average of 151.5p – the most expensive in Europe – while in Northern Ireland the price is 141.9p, the RAC claimed.
Its head of policy Simon Williams said: “Margins are once again staying persistently high, and drivers are paying the price.
“Our data clearly shows that pump prices haven’t fallen in line with the reduction in wholesale prices, so drivers across the UK – with the exception of those in Northern Ireland where fairer prices are charged – are once again losing several pounds every time they fill up.
“We believe there’s no good reason for retailers in Great Britain not cutting their prices at the pumps far further.
“We can only think they’re hoping no one will notice due to the distraction of the general election.”
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The RAC said retailers’ margins – the differences between what they paid for fuel and the pump price – were 14p per litre for petrol and 16p per litre for diesel.
The long-term average for both fuels is 8p per litre.
Mr Williams said the firm hoped the Competition and Markets Authority (CMA) is “aware of what is going on and will use this to bring retailers into line as soon as it’s able to”.
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An investigation by the regulator into supermarket petrol station prices found last year that increased profit margins had led to drivers paying an extra 6p per litre for fuel in 2022.
In March the CMA said margins remained “concerning”.
Prices are usually cheaper in Northern Ireland than in the rest of the UK, partly due to competition from forecourts in the Republic of Ireland.
Independent fuel retailers have said higher business rates, energy bills and wages have all contributed to higher costs.
Sky News has approached the CMA and the Petrol Retailers Association for comment.