I live in the UK and recently had some building work done (replastering, new light fixtures, new switches, laminate flooring, etc). During the work the builders discovered a lot of dodgy electrical stuff and fixed things as they went. However, after the builders left we discovered a strange electrical problem.
Sometimes (but not every time) when we switch on the light in the kitchen it causes the power for the whole house to trip out. It doesn't happen every time but it does occur fairly often - I would say there is 50/50 chance.
The switch that causes the problem was not changed during the building work so I don't understand how it can affect it.
The builders have been back out and double checked the light switches and fixtures and say all looks ok. They say they cannot do anything about it because it doesn't happen every time. The only solution, they say, would be to re-wire everything all over again.
Here's a photo of my breaker: