TOTP did got through a period when everybody had to play live, I think it was so bad the soon abandoned the idea, shame they never show those performances, the story I heard was the band were required to record the backing track during the day (union rules) so they could mime to it on the show, the Beeb turned a blind eye so management could swap the tapes for the recorded versions afterwards, I think some bands took the fosters because they objected to miming, certainly Jimmy Pursey (Sham 69) insisted on singing live to a backing track, hence the intro "look who's on top of the pops mum"