Help request - Bush TV very strange fault

My mum's Bush CRT TV developed a very strange fault yesterday.

Basically, it will switch into standby itself after about 1 minute if you are watching BBC channels, i.e. BBC1 & BBC2. This does not happen if you are watching ITV, CH4, CH5, but it does happen if when you are watching BBC through her Telewest (Virgin) cable box.

I could not understand how this selective viewing could be possible, so I retuned the TV so that BBC1 was on channel selector 3 and ITV was on channel selector 1. Believe it or not the fault followed BBC to channel selector 3.

So in summary, the TV switches itslef off if you are watching BBC1 or BBC2 (did not try BBC3 or 4), but is OK for all other channels - some weird type of censorship??

Any ideas?

Thanks
Ian.