- The Security Service was founded in 1909, during the buildup to World War I. At this time, it was headed up by Captain Vernon Kell, who remained at this position until the early years of World War II.
- The Security Service protects Britain's parliament, economic interests and the British people from terrorism, espionage and other threats to security. To do this fully, it works alongside MI6, the Government Communications Headquarters and the Defence Intelligence Staff.
- The Security Service's headquarters have been at Thames House in London since 1995. Nine smaller offices exist throughout the UK, including Northern Ireland and Glasgow.
- "MI5" was the Security Service's official name for only 13 years -- from 1916 to 1929. It is still referred to by this name today and, to acknowledge this history, MI5 appears on the official website of the Security Service.