After we moved into the new house, about a week after we were looking for the outside light switch... Finally found it and the garden area lit up - for about ten minutes.
Then everything went black. Checked the Consumer Units (we have three or four if you count the one in my Man Cave) and nothing had tripped...
Ended up walking up the road (100m) to the main fuse box which had tripped - 3 x 35A breakers in there.

Needless to say, the outside lights have not been switched on again...
Electrician is on the list anyway to upgrade everything to latest standards (is it 30mA or something now?) but until then we live with it...