I filled my diesel Jaguar XF with unleaded fuel. I drove it 400 metres to my house with no problem. In the morning I had difficulty starting it. When it eventually fired it ran rough for approximately 30 seconds before the problem dawned on me. It was then towed to a Jaguar garage. They advise that unless the complete fuel system is replaced (£7,000) the warranty will not be valid. The car is six months old.

A friend has told me of a similar mishap with his Mercedes-Benz two years ago. He called out the AA and they told him not to take it to a Mercedes-Benz dealer as they would insist on a full system repair. The AA man said that this was basically a scam by main dealers and advised flushing the system by the AA. This was done and no problems have arisen. In such cases is it necessary to replace the whole fuel system or is flushing out okay? Is the threat of loss of warranty being used by main dealers to justify an unnecessary work?