Britain’s biggest supermarkets are ripping off motorists with their local pricing policies for fuel, according to the country’s largest motoring organisation.

The AA last night urged government ministers to launch an investigation into the “postcode lottery”.

Edmund King, AA president, said that because supermarkets such as Tesco only pledge to offer the cheapest petrol price in the local area, the prices they charge can vary dramatically according to the level of competition.

He said that only towns with an Asda, which operates a national pricing policy, appear to be sure of getting the cheapest fuel on the market.

The AA fears that the huge variations in price mean that motorists in the south of England are effectively helping to subsidise cheaper prices in the north where there is a far greater number of Asda stores.

While Tesco charges 106.9p per litre for unleaded in Bury, Lancashire, where there is an Asda, it charges 7p more in Waltham Abbey, London - where the nearest Asda to is seven miles away. J Sainsbury charges 106.9p per litre in Dundee, but 4p more in Wembley.

Mr King said: “Is it fair competition that one chain is charging a price in one town but charging more just down the road in another?

“Drivers ask does it really cost more for a tanker to deliver the same fuel to a town just a few miles down the road? If there’s one price for a Mars Bar, why can’t there be one for fuel?”

He added: “It’s becoming a major issue and we are hearing from more and more MPs who have postbags that are bursting with letters from angry motorists.

“The government need to look at this and end what is little more than a post code lottery.”

Petrol prices have soared in the past year on the back of the rising oil price in yet another strain on household budgets.

The Bank of England claims the rising cost of fuel is a key reason why the official inflation rate is at its highest level for 16 years.