DRIVERS can't run their diesel cars safely on ordinary cooking oil, warns the AA.

The association is concerned that recent reports of drivers using it to evade fuel duty may encourage more people to try it - with potentially disastrous consequences.

John Stubbs, the AA’s head of technical policy, said: "Quite apart from the fact that running a car on cooking oil is illegal unless road fuel duties have been paid, it is simply not capable of protecting modern diesel engines from damage unless it is properly refined.

"Using recycled cooking oil is even more unwise unless it has been properly cleaned and treated. It is also classified as a waste and its use is covered by legislation.”

Peter Clery, the chairman of the British Association of Biofuels and Oils (BABFO), says: "Vegetable oils can be made into a perfectly usable fuel, biodiesel, but it must be correctly manufactured. Normal diesel fuel and biodiesel are refined to strict quality standards and have closely-controlled physical and chemical properties, essential for sound performance from modern engines."

The AA says that cooking oils are thicker than normal diesel fuel and will cause damage to the fuel injection pump and fouling of the fuel injectors.