St. Winifred's School Choir - There's No One Quite Like Grandma
This sickly sweet 80s hit reached #1 for two weeks from 27th December 1980. It features the ex-Coronation Street start Sally Lindsay - can you spot her? Although a very irritating song, at least the kids in the 80s were singing about Grandma, rather than mugging her!
Not quite a one-hit wonder, though, as they also provided the backing vocals to Matchstalk Men and Matchstalk Cats and Dogs by Brian and Michael which was also a #1 in 1978. That particular song was about the artist J S Lowry.