This clip is from an Omnibus shown in 1979 (or 78 without checking). The name of this short film was: "Disco Delights, Or What A Way To End It All" by David Richardson. The main film shown was "The People's Park" a documentary about Central Park, New York and this short was tacked on the end.
it was fairly short and focused on "northern discos" and featured heavy rock, "Roxy" and Northern Soul, I watched it at the time and the music that was playing while the clip was on was definitely Afternoon Of The Rhino. Whether this was what they were dancing to in reality I can't say. I think Interplay was the intro music to the whole short film
Edit - it was 1978