[sheerwater]

Government new development. Instead of speed cameras they disable your car in the most inappropriate place to cut your average speed down. The only other method they use is gridlocking our motorways. Seriously though I had a friend with a 740 with approx same problem. His turned out to be plugleads which at the slightest hint of damp/ rain etc cut the car out. WD 40 didnt do the trick. New plug leads. No problem.
Seems to be a funny fault with the carbon type plug leads as they get older. You could also try the old trick for seeing if there is a problem. Find a really dark spot and start engine. Look for little blue flashes where the leads are short circuiting. DONT do what friend did and touched the plugleads. He still has the dent in the bonnet where his head hit it!!!!! Sorry no more help. Nigel