Ok looks like the problem has been solved.
The solution was to wire the fused spur off the same RCD as that which supplies the ASHP and the pump's wiring centre. Now when I switch things on and off no tripping. Apparently caused by differential as previously two different circuits were being used, the RCD is on 30ma and therefore ultra sensitive and prone to tripping out.
I'm pretty sure that the solution is what a few of you suggested, so many thanks for letting me air my frustrations and your help which is very much appreciated.
Rob.
Think Desp' and me can claim our prize ??
