I've fixed hundreds of faults, not come across this one. It sometimes happens when there is a fault at the transmitter end, which is then fixed by the technicians - if this is so it will right itself. If not, if the TV has separate tuning buttons, try tuning another button in to BBC2 - I had this fault recently on an old set. If this is cures it, the set needs cleaning inside the tuning area. If your set tunes itself in, perhaps the aerial? Try plugging in a temporary set top aerial to test this. If this cures it, check all aerial connections for shorts etc.
John Davies, June 2004