Both supermarket giants have cut their prices by 2ppl as of today (9 July), with Avishai Moor, Sainsbury’s head of fuel, saying “This is another great piece of news for our customers today, following the announcement that fuel duty will remain at the same level this year. Fuel can be a big expense, so we’re proud to be offering our customers great value for money when they fill up with Sainsbury’s.”

Peter Cattell, fuel director for Tesco, said: “With summer holidays just around the corner, we're helping our customers to get away with their families by dropping the cost of diesel by 2ppl at all of our 500 filling stations.”

The news came as the Chancellor announced yesterday that fuel duty will remain frozen.

However, research by the RAC last month found that drivers were still paying 3p a litre more for diesel, despite the wholesale price of diesel being cheaper than petrol for all of June.

Commenting on the announcements by Tesco and Sainsbury's, RAC fuel spokesman Simon Williams said: “This is welcome news for diesel drivers and businesses and is exactly what our RAC Fuel Watch monitor has been calling for. 

“The wholesale price of diesel has been significantly lower than that of petrol throughout June. We believe that there is scope for at least a 5p cut in the price of diesel, which will be the first time that motorists have seen diesel cheaper than petrol at the pumps in almost fifteen years.

“This is a bold step by Tesco and Sainsbury’s and we are confident that they will be swiftly followed by other retailers making even deeper cuts, and should lead to a fundamental re-balance of pricing in the retail fuel market. We need greater transparency and a fairer pricing model for both petrol and diesel and this is likely spell the end of the focus on petrol prices alone.”