RedY2KS2k like the suggestion I'll bear it in mind my travels.

 

It appears that my problem wasn't linked to the starter motor, but a symptom of the immobiliser circuit board failing. I guess the electrics running through it caused a problem heating it up, leave the car sitting for a while, it cools down and works.

I found out thde hard way when the system finally gave up on me and I was left with a car that wouldn't start, though I did also experience a different symptom of 'turning over' but not firing. I believe caused by the fuel pump being immobilised. But both are symptoms of the board failing

Thanks for all your suggestions