Well, all solved! A brilliant mobile auto-electrician called Mark Eaton came to see the car and did the usual checks - he found that the coil was getting 5 volts from the live feed and so went looking for a wiring problem. The answer was some loose wires on the under surface of the under bonnet fuse box. Push them home properly and BINGO! starting problem solved! The car now starts first time, every time! The previous two electricians picked on the coil and the ECM as the culprits, but mistakenly so. As aresult I now have two new coils spare, plus a new ECM and the engine management EEC as well! Oh, and a distibutor cap, rotor arm and a set of plug leads! Logic and common sense fly out of the window when you're clutching at straws.......
Many thanks though to all of you who made suggestions as to the solution. None of us thought of the real answer!