Please Sir! - The Fen Street Gang - Bowler
Till Death Us Do Part - Till Death ... - In Sickness and In Health - The Thoughts of Chairman Alf
How about Peter Bowles and Penelope Keith both starring in To the Manor Born and Executive Stress - albeit as different characters?
The Detectives sketches in Canned Carrott and the series The Detectives.
The Blackadders might be one, but I think we're all agreed that's a series, not an ancient version of 7Up.
The Fall and Rise of Reginald Perrin - The Legacy of Reginald Perrin - Perrin
Man About the House - George and Mildred and Robin's Nest
M*A*S*H - After M*A*S*H
The Phil Silvers Show - The New Phil Silvers Show