Seems Vauxhall think it's something to do with the Heating & Vent system but do not have a definitive fix since the models which present the problem are burnt to buggery.
Here's the facts as they happen:



I remember the self-igniting 406's but only one member here had a problem (miniman) but this Vauxhall problem seems worserer. If I was to guess I'd say it was an over-heating electrical connector on the cabin fan motor. Or something.