Collected my car back today. They said there was a small silver thing attached to the fuel pump; looked like a suppressor or something. It had two wires going into it, giving 12 volts and two wires coming out of it, into the fuel pump, giving 12 volts. They couldn't see the reason for its being and bypassed the wires round it, straight into the pump and it works fine!
Might take the cover off myself at the weekend to see what they are talking about.
Anyway, my car is back on the road now. New head gaskets, heads reconditioned, turbo reconditioned, new exhaust and MOT passed (eventually!).