For me it’s Benny Hill’s #1 hit single Ernie.
Jasper Carrott’s #5 hit “Funky Moped” mostly sold because of the B-side but it’s still an interesting listen.
Vic Reeves got to #1 with “Dizzy”, but that was a cover version of another artist’s song, so I’m not sure it really counts. It is very enjoyable, though.
Baddiel, Skinner and the Lightning Seeds got to #1 twice withThree Lions, but the Lightning Seeds were a real mainstream band.
Are there any you like in addition to those?