Drivers have been paying more for fuel since 2019 due to weakening competition between retailers, a regulator has said.
They said that increased supermarket fuel margins led to drivers paying an extra 6p per litre.
Asda has also been fined £60,000 for a failure to provide information when required, the regulator added.
It comes in the Competition and Markets Authority’s (CMA) final report in its year-long investigation into the fuel market.
As part of the investigation, the watchdog examined whether there was “any failure in competition” which was leaving consumers paying higher fuel prices than they should be.
It had previously said supermarket fuel prices were roughly 5p more expensive per litre in 2022 than pre-pandemic levels and that factors beyond the invasion of Ukraine have impacted the price customers are paying at the pumps and weak competition has helped drive increases.
Supermarkets in particular came in for criticism.
“Higher pump prices cannot be attributed solely to factors outside the control of the retailers,” the CMA said.
On Monday morning, the Petrol Retailers Association (PRA) told Sky News that independent forecourt operators have struggled to be competitive against supermarkets.
In March of this year, the CMA identified 13 areas of concern as part of Asda‘s plan to buy Co-op petrol stations and requested the supermarket buyer take remedial action.
A similar investigation into competition and food prices is being done by the CMA.
Chancellor Jeremy Hunt last week met with regulators, including the CMA, in an effort to push suppliers to reduce prices.