"Detective Waiting" (1971).

Richard Beckinsale in "Detective Waiting"

In this 14 September 1971 episode of Armchair Theatre, unpopular young detective Lewis (Richard Beckinsale, father of Kate) has a lot to prove to his skeptical colleagues when he is assigned the task of getting the goods on a slippery criminal. The screenwriter is Ian Kennedy Martin (The Saint, The Sweeney).