Thanks for the responses folks. I guess rotten eggs is the best answer to anyone who doesn't,t know what a chemical works smells like. From Teesside myself, that is smoggy land. Lol Anyway not happening when reversing, and has only happened the twice,not at all in last two days trips. Holiday in Derbyshire at the mo. Read a couple of articles that mentioned cat converter,so a possibility,definitely not air con as certainly haven,t used it,don,t think it even has it. Wife,s car, and only basic model, she won,t pay for what she calls gadgets,just wanted a cheap reliable vehicle! Agree with the poster though who said they had a bloody awful smell,because it certainly was,not something you could mistake or imagine,and anyway on both occasions there were two of us in the car. First time was parking in a car park in Chesterfield, and we just put it down to the Towns smell,not really associating it with switching off. (Apologies to any Spireites around) second time was at Chatsworth. Thanks again,not at the moment overly worried,well at least until it re-occurs.