All was fine until 3 of the bulbs blew. Got replacement bulbs and now they keep dimming. They'll be on nice a bright for about 20 mins and then dim for about 10 mins.
If all of them dim simultaneously it suggests a (weird!) problem with the power supply, rather than with the lamps themselves. If they're on a dimmer switch it might well be time to replace it.
If not, I suspect you may have accidentally turned the guts of one of the bulb-holders (those GU10's are a bastid sometimes) and a wire is now touching something it maybe shouldn't.
"Is it possible that he did something when he was putting them in ...?"
Like I said, he 'may' have turned one of the bulb-holders inside the light fitting. That 'might' cause a problem with the wiring on the back of the bulb-holder.
When the sparky came round to put the light fittings in the kitchen he went to the fuse box and was gob smacked. He said that if it wasn't for the fact that he's mates with my cousin he wouldn't have touched it...(he made it safe for us)
The sparky before that couldn't do anything because he'd never seen anything like it and didn't know what to do...lol
When I bought my house I looked at electrics...heating systems etc...
When he bought this house he looked at the proximity to the pub...lol