The report found the rise was instigated by Asda  – which was also fined £60,000 for not co-operating fully with the CMA investigation – and Morrisons, the two cheapest fuel sellers, which last year each made the decision to target higher margins. 

Asda’s fuel margin target in 2023 was more than three times what it had been for 2019, while Morrisons doubled its margin target in the same period. 

Other retailers, including Sainsbury’s and Tesco, didn’t respond “in the way you would expect in a competitive market” and “instead raised their prices in line with these changes”, the CMA found. 

“Taken together, this indicates that competition has weakened and reinforces the need for action,” the report added.

Diesel prices have also been slow to drop in 2023, partially down to Asda ‘feathering’ its prices (reducing them more slowly as wholesale prices fell) and other firms not responding competitively to that. 

The CMA estimated that drivers have paid 13p per litre more for diesel from January 2023 to the end of May 2023 than if margins had been at their historic average.

“Competition at the pump is not working as well as it should be, and something needs to change swiftly to address this,” said Cardell.