On Christmas Day in 1965, the Doctor, Steven, and Sara Kingdom - and a certain Iris Wildthyme - all were present at a police station in Liverpool. The station was owned by Liverpool City Police.
History
During their adventure with the Daleks and Mavic Chen, the Doctor materialised the TARDIS outisde the police station. A policeman, (TV: "The Feast of Steven") called Ellis, (PROSE: The Mutation of Time) observed the TARDIS, suspicious of it. A policeman and his partner, (TV: "The Feast of Steven") Welland and Blessed, (PROSE: The Mutation of Time) arrived in their patrol car, and he directed them to watch the police box whilst he referred the matter to the Detective Inspector, (TV: "The Feast of Steven") Windsor. (PROSE: The Mutation of Time)
Welland saw the Doctor quickly exit the TARDIS, who was attempting to fix a scanner. As soon as the Doctor saw Welland, he re-entered the TARDIS and locked the doors behind him. Welland told Blessed on this, but Blessed didn't believe him. Welland was proven correct moments later when the Doctor exited the TARDIS again, who intended to distract the duo so that Steven and Sara could fix the scanner. Welland and Blessed then took the Doctor inside the station.
Inside the station, the Doctor saw a group of policemen, with a man in a mackintosh telling them about a vanishing greenhouse. The Doctor mentioned to this man that he looked familiar, much to the man's bewilderment. Outside, Steven sneaked past one of the guards, and donned a police uniform he found, and entered the station wearing this disguise. The Doctor had been very truthful with the police officers when they asked him questions about who he was and what was the mysterious police box, and they deemed him mentally unstable. Just as they were going to place him somewhere secure, Steven comes in, still disguised, and takes custody of the Doctor claiming that he is from G Division. The trust him, and hand the Doctor over to him.
Outside, Welland had found Sara outside the TARDIS, and fairly asked her to move along instead of just arresting her. Steven and the Doctor arrived, and they rushed back into the TARDIS, and it dematerialised. (PROSE: The Mutation of Time, TV: "The Feast of Steven")
According to a letter to Panda written by Iris Wildthyme, she had been also locked up in "the slammer" with "someone who looked like the one off Upstairs, Downstairs", who told Iris that "this one had been junked". Iris had then admitted that she had then pulled out a bottle of sherry, with everything after that being hazy, with only some memory remaining of running around in a silent movie and escaping through the Fourth Wall after someone did a toast through it. (PROSE: From Wildthyme with Love)
Behind the scenes
Originally, during the production of TV: The Daleks' Master Plan, it was intended for "The Feast of Steven" to be a crossover with Z-Cars; however Z-Cars producer David Rose shut down the idea. However, the Liverpool setting of the police station remained.
In From Wildthyme with Love, Iris is clearly claiming to have been present during "The Feast of Steven", despite her account not exactly lining up - this can be simply explained by the fact that she is mis-remembering due to the fact she got drunk almost immediately.