Motorists will benefit from lower supermarket petrol prices from today, but diesel prices will stay static.

First, Asda announced that it would be cutting up to 2p off a litre of petrol from this morning.

Then rival Sainsbury's announced a similar up-to-2p reduction which will also take effect from today. Tesco then said it would follow suit.

Asda customers will pay no more than 133.7p a litre for their petrol from today. Its diesel remains at 139.7p a litre.

Asda's petrol trading head Jeremy Walton said yesterday: "We always aim to be the first retailer in each part of the country to drop prices when costs are falling and the last to put them up."

Richard Crampton, Sainsbury's head of fuel, added: "We're always looking for ways to help our customers save money, particularly as we head towards the festive season, so we're delighted that from tomorrow we will be reducing our petrol price by up to 2p per litre."

And a Tesco spokesman said: "We are dropping the price of unleaded fuel by up to 2p per litre from tomorrow morning.

"As Britain's biggest petrol retailer with 490 forecourts, more motorists will make savings at the pumps at Tesco than at any other fuel retailer."

AA public affairs head Paul Watters said: "Last week, our fuel-price report pointed to a 4p drop in petrol wholesale prices working its way through the system.

"UK average petrol pump prices reached a late summer high of around 140p a litre in mid September and sat there for more than a fortnight. More than a month on, the average petrol price yesterday was down to only 138.70p a litre."

He said that the supermarkets' announcement was welcomed. But he added: "Unless the rest of the market reflects the lower cost, it's a case of the same old story - prices up like a rocket, falling like a feather."