I checked the
sensor today using a multi meter. I got a reading on OHMS setting but there was nothing coming up on the display when switched to AC volts.
I waved a magnet in front of it and got a reading.
Then i cleaned the contacts with curcit-board cleaner.
Refitted it on engine and reconnected the plug, traced wires to where they were more accessible in loom (round the bell-housing under the radiator pipes) .
Re-connected multi meter and cranked engine and it started.
I left the engine running foe 30 mins to get it realy hot.
Turned it of then re-cranked it and went for a 10 mile drive to re-calibrate
It now runs and starts every time and the STOP light on the dash has gone.
Thanks for your advice, and hope this also helps anyone else that has the same problem.