Bit more research, I think now it's a Two Ronnies musical interlude from 1985, even though the single and album had been released 2 years earlier. The Stages album had a bit of a revival in 85 after IKHSW had been No 1, so during this series she sang a selection of songs from it. It's not the Val Doonican set, I've seen other vids from that series since.
Not mad about this rendition , this is not a pop song . I was lucky enough to have sung in the chorus recording at The Royal Festival Hall performance with Johnathan Pryce I have loaned it out ages ago Must get it back !! it is magnificent !
I came here thinking I'd see a raw, emotional take similar to Paige's very human Grizabella. But you're right - it's pop! It's not even disco. Disco has more soul than this..