It is possible that someone in the house has replaced one of the bulbs, though they are all away at the moment. I have just removed all of the three bulbs (Tesco Value 12v 50w - whoever it was is a cheapskate!!).
The filaments on them all seem to be alright.
Our sitting room ceiling light is a three bulb halogen fitting. Last night they just popped off, so I unscrewed the fitting from the ceiling and removed the fuse, a 630mA 250v glass fuse.
The fuse had blown so I bought three today and replaced it. I turned on the light switch at the wall and...