Ok after spending much of the day tracing around the electrics of the car, I think I've solved the problem! Not quite sure *what* the problem was, but wherever I've found an electrical contact, I've recrimped and reshielded it (high temperature cable shielding). Yes, it is probably the long route around the problem, but I've learned a lot about a fiesta's electrical layout!!
I'm happy to report that the car is now running absolutely fine, and the car is booked on the 24th November to have its tappets fixed. The garage reckon that this work will cost about £45.
Im also considering a new car, a Toyota RAV4 or a Ford Focus. Anyone got any comments on either of these models? Or recommendations on other cars: big/small car, diesel/petrol, decent response, decent handling, less than £7000 preferred (not a requirement). Preferably with decent security gear built in, but not a necessity.
Oh, and why dont cars have lights built in under the bonnet? It would help in case you ever break down at night.
Ok, I've opened a few new threads in this. I'll move this post to a new thread.
Once again, thanks everyone!