Hallamshire Police was the English police force responsible for the Hallamshire area of South Yorkshire, including the city of Sheffield, where their headquarters was located.
Yasmin Khan, companion to the Thirteenth Doctor, was a probation constable with Hallamshire Police. Other officers included Sergeant Ramesh Sunder, Khan's superior officer. (TV: The Woman Who Fell to Earth)
Yaz did not advance past her probationary period for some time, as she was often called away by the Doctor or her allies. Ramesh urged her to spend more time with them. He called Yaz their "best probationary officer". (TV: Spyfall) By the time that the Flux ravaged the universe, Yaz had left the police force. (TV: The Halloween Apocalypse)
Behind the scenes[]
In the real world, the police force covering the Hallamshire area is the South Yorkshire Police.
Although certain parts of the episode The Woman Who Fell to Earth were filmed on location in Sheffield, exterior scenes of the Hallamshire Police Headquarters were actually shot at the South Wales Police Cardiff Central Police Station in Cardiff, Wales. This location was revisited for Spyfall, as well.