As a tribute to the Doctor Who actor who played Sgt Mike Smith who died of AIDS.
“Russell T Davies wrote the character of Richie played by Olly Alexander as getting a part on the TV show Doctor Who, and filming a scene with Daleks. You can take the man out of the TARDIS, but you can't take the TARDIS out of the man. The show is also being produced by Phil Collinson who also produced all of Russell T Davies' Doctor Who. And the director is Peter Hoar who directed Matt Smith episode; A Good Man Goes To War.
The show sees a scene from the Peter Davison Doctor Who story Resurrection Of The Daleks with a little of the Sylvester McCoy Remembrance of the Daleks, recreated as the fictional Regression Of The Daleks for It's A Sin, with a Dalek/human shootout in space ship airlock, with Olly's character cast as one of the humans, Trooper Linden, rather than a Dalek operator.
Russell T Davies tells Doctor Who Magazine #560 that it's not just some kind of an in-joke for him, but a memorial for Dursley McLinden, who played RAF Sergeant Mike Smith in Sylvester McCoy's Doctor Who. who died of AIDS-related illnesses in 1995. "He became very wonderful in his AIDS activism when he was ill," Russell remembers, "but to me, he was that boy from Remembrance of the Daleks. That's why I knew I had to write a Dalek scene in It's a Sin. I didn't do it as a joke. it's not me going, 'Hooray, let's get a few pages in Doctor Who Magazine.' It, literally, felt natural. I was really desperate to do it. It's a little smile towards Dursley, who I loved. I did it for Dursley."