In BBC’s Sherlock, which organization runs the prison at Sherrinford?

In BBC’s Sherlock, the prison at Sherrinford is run by the British government.

Sherrinford is presented as an exceptionally secure island prison holding dangerous individuals, including Eurus Holmes. Mycroft explains that the facility is controlled by the British government and kept outside ordinary public scrutiny.

The prison becomes central to “The Final Problem,” the last episode of series 4. Sherlock, Mycroft and John travel there after learning that Eurus has manipulated events from inside the institution. Its isolation and security help explain why Eurus’s activities remain hidden for so long.

Sherrinford is not the same as Scotland Yard, which is associated with London’s Metropolitan Police and Inspector Lestrade. It is also not an MI5 or CIA facility in the show’s stated description. The government-operated prison is one of the series’ major original additions to the Holmes mythology.