No it was caused by the 'Pace Car' which sped off the cars at the back thought the race had started as the pits were coming up but the pace car had not pulled off the race mode cars caught the non race cars and the rest is a very very sad pile of some of my favourite cars........
Thanks for the explanation Paul - I suppose the saving grace is that (assuming they are) race cars are generally more rebuildable than the road going equivalents!