Motorists were last night warned to expect petrol prices above £4 a gallon after the cost of oil moved within touching distance of 50 US dollars.

Fresh attacks in Iraq overnight added to the jitters of traders and sent the price of a barrel of oil to a record high of 48.98 dollars.

The average cost of a gallon of unleaded petrol is currently £3.71, or 81.7p a litre, meaning the annual cost of filling the tank is £150 higher than in January.

The AA motoring organisation said motorists faced a ''roller-coaster ride'' over the next few months as rising interest rates compounded the sky-high cost of crude.