CAT III
Thanks for taking the time to read and reply.
Certainly not obvious - I had a hunch to check the sockets in the conservatory which lost a roof panel in high winds a few weeks ago and although promptly replaced some rain got into the conservatory. The first socket I opened had a rather shocked slug sitting across the earth and live connections with loads of slug slime around him to make a good contact. I have no idea how he got in there.
Conservatory circuit disconnected and all is well. I will get qualified electrician in after weekend to check circuit and replace slimed socket.
SWiMBO told me I'm not off decorating duties!
srobarts