SOLVED:
Big shout out of THANKS to AutoGeek on the SwedeSpeed forum who told me about the 'secret' swedish method of battery reconnection in a P1 volvo, being " place the key in position II, reconnect the battery, key to position 0."
I started out today with the battery installed and the car would not start, even using the method recommended. So I disconnected the battery, then I put the key into position two and only then did I reconnect the battery - there was a healthy spark and I could hear the throttle body cycling. Then I turned the key to position 0 removed then reinserted the key and twisted to position 3 and the car burst into life.
So my drama is solved, lesson learnt and some experience gained. It only took 4 days!
Thank you to all who contributed. ?
Martyn