Thanks for all info.
It has been going on for some time we went away at Xmas expecting it to trip but surprise nothing until we got back. When we were away we left nothing on standby so maybe it is something to do with that. We had thought of getting the circuit board changed.
The weather...
For some time we have had a problem with our mains tripping for no apparent reason. The circuit board does not trip any individual fuse just the complete mains. It can happen as recently as 3 times in as many days or nothing for a month.
Any ideas please?