Hi weasel 56 X,thanks for quick reply,dipstick clean, oil looks clean,car has 44,000miles, service due 600miles,car never abused.wife had music playing loud so bang was like big misfire followed by white smoke,she stopped quick.coolant seems ok.car started 4 times since fault,runs slightly rough,lots white smoke, smells bad .i understand engine management designed to overfuel under certain circumstances. She just told me that car was revving higher than usual pulling up hill around 3000 rev then shifted up gear on auto when misfire occurred.