From that strange twilight period on TOTP in late 1976: the Pan’s People - Legs & Co. interregnum, when hybrid dance troupe Ruby Flipper flourished briefly. Here they are, dancing to the appalling Disco Duck by Rick Dees & his Cast of Idiots. Featuring some awful duck costumes, and some even more awful special effects.
10 August 2010: The video clip I'd embedded in this post is broken. I've found a much higher-quality version anyway, which I posted here.