Airing later this month, the one-off drama explores Isherwood’s formative years in 1930s Berlin in the run-up to the Second World War and co-stars Lindsay Duncan (Doctor Who: ‘The Waters Of Mars’), Imogen Poots (28 Weeks Later), Toby Jones (Doctor Who: ‘Amy’s Choice’) and Douglas Booth (Worried About The Boy).

Smith told BBC Press Office: “Well, you’ve just got to commit to it, gung ho. It’s different from when you’re doing nude scenes with a boy than doing them with a girl, as you can imagine. But I tried to commit to it and wholeheartedly go for it.”

He added: “Having to kiss boys, and finally understanding the nature of stubble rash, was interesting.”

Asked what attracted him to the role, Smith said: “The story is such a fascinating one. I loved the idea of playing someone so extreme to me, that different kind of vocalisation and physical shape. At the heart of the piece is Christopher’s acceptance of his own identity and self-discovery – I think we learn about a man exploring his sexuality and the arena in which he can do that freely.”