MI5 is a branch of the British government's intelligence division.
In 1997, the head of MI5 was Veronica Halliwell, who was ordered to shut down a publishing company which had released an exposé on UNIT. (NA: The Dying Days)
In 1998, Halliwell was assassinated by the Voracians. Her death was investigated by fellow MI5 member Harry Sullivan. (MA: System Shock)
In 2006, Margaret Blaine, whom the Slitheen killed and used as a bodysuit, was a member of MI5. (DW: Aliens of London)
In 2009, Thames House, the MI5 building, creates a case filled with gas for The 456. The building is locked down and those inside are killed by a virus which is released into the air. (TW: Children of Earth)
