The move comes just days after criticism from the AA that fuel retailers had been “plundering” diesel car drivers by up to 6p a litre.
Wholesale diesel prices have been 2p below petrol for the last six weeks, so it will be of great relief to motorists that forecourt prices are starting to reflect the difference.
The Morrisons price makes diesel cheaper than petrol for the first time in 14 years, Sky News reports.
Since January 2014 wholesale diesel prices have fallen by 44 per cent to around $535 (£343) per tonne. But over the same period, prices at the pump are down just 14 per cent.
The fall in wholesale prices can be attributed to weak demand across Europe twinned with an increase in diesel refining capacity.
The day after George Osborne’s summer budget, in which he announced the freezing of fuel duty, the big four supermarkets on average trimmed 2p per litre off the price of diesel across their combined 1,400 filling stations.
According to the website PetrolPrices.com, the average cost of a litre of diesel at a UK filling station on Thursday last week was 118.21p, while the lowest available price was 112.9p. The highest price offered was 134.9p per litre.
Although diesel cars only comprise 37 per cent of all cars in Great Britain, half of all new cars sold here are diesel.
Mark Todd, Petrol Director for Morrisons, said: “Because of the recent price drops in the wholesale diesel price, we are able to pass on these savings to our customers.
“This is a milestone in motoring and many younger drivers won’t remember the last time that diesel prices were lower than unleaded.
“While we are cutting diesel prices today, we will continue to look for opportunities to pass on savings on unleaded as soon as we can.”
A small number of Morrison’s 336 petrol stations will still see diesel prices higher than petrol ones as a result of “local competitive factors”.
Earlier this summer the Supreme Court ruled Britain must plan immediately to reduce nitrogen dioxide levels to meet EU targets.
As nitrogen dioxide is mainly produced by diesel engines, controls or restrictions on diesel cars in British cities could be enforced.