A lack of competition from some supermarkets on fuel has allowed independents to undercut the big boys over the past few months.

AA president Edward King told The Grocer that retailers such as Shell, Jet and others had recently undercut one and sometimes two of the big retailers. And considering that he praised Asda and Morrisons as the drivers of falling prices, it's clear he was referring to Tesco and Sainsbury's.

"The willingness of some supermarkets to compete on fuel prices only where they have to is creating a golden opportunity for independent fuel retailers to undercut them," he said.

King also complained that as fuel prices spiralled towards the end of last year and the first few weeks of 2010, the "cross-supermarket level of competition has diminished significantly".

Tesco rejected the idea it was no longer competitive. "Our aim is to be competitive on the price of fuel in the catchment area of every one of our stores," said a spokesman. "Customers know Tesco will be the cheapest in their area."

King's comments come the week after The Grocer revealed that Asda, which has always lambasted rivals for not operating a national pricing policy, had price fluctuations of up to 3ppl for unleaded petrol and 2ppl for diesel.

Asda wanted to operate a national fuel policy, but could not offer the same price at each forecourt until "our competitors stop messing around", a spokesman said. When Asda reduced prices, it tried to move all stores to the same price and "ensure we're always lowest when prices are rising", he added.