Colditz.S1E10.Tweedledum

Colditz is a British television series co-produced by the BBC and Universal Studios and screened between 1972 and 1974.
The series deals with Allied prisoners of war imprisoned at the supposedly escape-proof Colditz Castle (Oflag IV-C) during World War II, and their many attempts to escape captivity, as well as the relationships formed between the various nationalities and their German captors.
Colditz was created by Brian Degas working with the producer Gerard Glaister, who went on to devise another successful BBC series dealing with the Second World War, Secret Army. Technical consultant for the series was Major Pat Reid, the real British Escape Officer at Colditz. One of the locations used in filming was Stirling Castle.

Written by John Brason
Wing Commander Marsh (Michael Bryant), an assistant to the British Medical Officer, decides to use his extensive knowledge of mental illness for an escape. He proposes to "go insane" and be repatriated. Colonel Preston agrees to let him, so long as he follows through with it to the bitter end.

Alex4History supplementary note:
The method of escape is based on that used by Ion Ferguson, a Royal Army Medical Corps doctor imprisoned in Colditz, who certified a number of prisoners as insane in Stalag IV-D, who were then repatriated to Britain. Ferguson then feigned his own insanity to gain repatriation in 1945. Ferguson detailed his escape in his account of his wartime experiences, Doctor at War, and the episode, Tweedledum, is a fictionalised account of his means of escape retold as tragedy.

https://en.wikipedia.org/wiki/Ion_Ferguson