Diesel, the fuel used by most freight operators and four out of 10 car owners, is also being cut. It will come down by 4p a litre to bring it in line with unleaded for the first time in three years. The discounting will bring much needed relief to drivers who were warned last week that the 90p or even £1 litre of petrol was on the way following a spate of terrorist attacks in Saudi Arabia, the world's leading oil producer.