The Cuckoo Waltz

The Cuckoo Waltz was a 70's sitcom starring Diane Keen (The Feathered Serpent, Rings On Their Fingers, You Must Be The Husband, September Song, Ruth Rendell Mysteries, Doctors) and David Roper (Harry, EastEnders) as a young couple who take in a lodger to help make ends meet. The lodger was played by Lewis Collins (The Professionals, Cluedo) in the first 3 series and by Ian Saynor (The Mallens, The District Nurse) as a different lodger in the last series.
http://en.wikipedia.org/wiki/The Cuckoo Waltz