The CMA said that in prior years fuel had been relatively competitive because supermarkets such as Asda and, to some extent, Morrisons had led with lower prices.

However, Ms Cardell said: “Asda decided to increase the fuel margins that they wanted to get and instead of seeing any kind of competitive response from other retailers, all the other retailers let their margins drift up at the same time.”

It is “drivers who have paid the price” for this, she said.

Last year, the CMA released a report that noted Asda and Morrisons were both purchased by private equity firms in 2021, which was the same year the supermarkets made a decision to increase their target margin on fuel.

Asda was bought in 2021 by brothers Zuber and Mohsin Issa and TDR Capital.

The billionaire Issa brothers bought half of the supermarket for £6.8bn and also own hundreds of petrol stations.

Morrisons was bought by private equity firm Clayton, Dubilier & Rice for £7bn in October 2021 after a bidding war.

The BBC has contacted Asda and other major supermarkets for comment.

The British Retail Consortium said: “Retailers will continue to work closely with the CMA and provide the necessary data to allow consumers to find the best prices for petrol and diesel.”