Restart.

Electronic advice works  with household electrics as well.  The outside floodlight went pop a couple of weeks ago and kept tripping the house boxes.  So aggravating was it looking for a replacement, that further investigation seemed the easier choice.   After some imaginative re-wiring up in the apex of the garage roof space to check whether the PIR or the light unit was at fault (neither seemed to be faulty), reassembled as originally wired and, BINGO! - all seems to be working again.