Once Matt Smith had finished filming his first series as "Doctor Who" (and escaped America after being stuck there by the Icelandic ash-cloud during the promotional trip) he went off filming a standalone drama in Northern Ireland. It's called "Christopher and His Kind", based on an autobiographical memoir by Christopher Isherwood of his life between 1929 and 1939, best known as the inspiration for "Cabaret".
I actually got the book out of the library around the time they were filming this. It's a very easy read, though mostly told in the third person (as the title suggests) as Isherwood obviously feels himself a different person by 1976.
Anyway, this looks like it's being marketed as the top drama in the BBC Two autumn season and Matt's co-stars include two recent "Doctor Who" guest stars in Lindsay Duncan (who also played his mother in "That Face") and Toby Jones.
Playing one of his love interests, Heinz, is teenage model-turned-actor Douglas Booth (who was great as Boy George in "Worried About the Boy" last May).