I am in dispute with Audi UK over the failure of a piston in the engine of my 2007/57 Audi S3. I asked for an RAC inspection as I did not trust the garage when they said the car needed a new engine at some £7k-£8k cost. The car has done not quite 18k miles but is out of warranty. The RAC inspector confirmed damage to the piston and exceeded his authority in discussing the issues with Audi Canterbury effectively destroying my bargaining position.

I am taking the matter up with the RAC independently. I have asked for any independent assessment of the plugs by a senior Mercedes service technician and he tells me there is no damage to the plugs. The garage that fitted the plugs says they are the correct ones for the car. Can you please advise me as to who I can pursue for liability. I thought it was the petrol / air mixture that determined whether the engine was running 'hot' and likely to damage a piston and plug rather than a defective plug being responsible. I suspect Audi of trying to pull 'a fast one'.