As this was the 1971 Christmas edition of TOTP, I think he was definitely the worse for wear due to the BBC's Christmas drinks hospitality, and had to leave the stage either to throw up, or because he was making a twat of himself. If you look at the clip of Ashton Gardner & Dyke performing "The Resurrection Shuffle" later on in the same edition, Ashton is so p*ssed that he fluffs most of the words (yes, a live singer on TOTP)!