The effects of Hurricane Katrina on US oil production appear to have been the trigger that sent the price of a litre of unleaded petrol towards the �1 mark.

But oil prices have been rising steadily, fuelled by a mixture of huge demand in China and India, uncertainty in the Middle East and limited US refining capacity.

Petrol retailers are hoping the rise might be a one-off and that prices will settle in the autumn, when demand tends to drop.