Well, it's still going on and I think the problem may be my Lumenition power module. I have a brand new ignition coil and when the engine gets up to running temperature (around 90-95 degrees Celsius) I get a weak or no spark and it won't restart.
The RAC guy (That's like an AAA guy for the American readers) who came out did a spark test and found no spark on the plug or from the coil. He said it's most likely to be the ignition module, he even commented that if I had a good old points and condenser he could have fixed the problem. He said that the solder on the circuit board inside the module could have dry joints and when expanded once hot it breaks the circuit. This would also explain why my last coil was fried, apparently.
The module at the moment is right opposite the Webers and under one of the sock filters (a placement I've never been happy about and will be relocating if I decide to replace it). When I removed it after getting home it felt quite hot to the touch.
I'm not sure whether to buy a new Lumenition module at around ?100, go back to condensor and points ignition (I'm not averse to the idea of setting the point gaps once a year - a small price to pay for reliability) or go for a new system such a Petronix Ignitor:
http://www.pertronix.com/prod/ig/ignitor/default.aspxI like the idea of the Petronix system not being prone to heat damage and all being hidden under the distributor cap with no 'black box'. If anyone has this system I would appreciate hearing their experience of it. The Lumenition can't be more than five years old as the previous owner had recently fitted it I believe. I don't really want to spend ?100 on another one if it has a <5 year lifespan. I've done a bit of web based research and it seems the power modules failing is not a rare problem.