Petrol prices are continuing to fall as the UK’s largest supermarkets cut prices for the second time in a week.

Asda, Tesco and Morrisons all reduced forecourt prices by around 2p a litre to bring the average cost of unleaded to 97.9p.

Tesco moved yesterday at “the majority” of its 430 forecourts, claiming its prices were now at their lowest for a year, while Asda made the change from today at more than 170 petrol stations operated by the retailer.

Last week Asda and Morrisons brought the cost of unleaded under £1 a litre for the first time this year with 2p reductions to 99.9p.

The news comes after prime minister Gordon Brown urged forecourt operators to pass on to customers dramatic falls in the price of oil, which has seen its value tumble by a half in recent weeks amid unprecedented economic upheaval.

“We expect oil prices to fluctuate in the coming weeks and will continue to pass on cost savings to customers whenever and wherever possible,” said ASDA trading director Darren Blackhurst.