The Balcombe Street siege was an incident involving members of the Provisional Irish Republican Army (IRA) and London's Metropolitan Police lasting from 6 to 12 December 1975.

In one incident the Guinness Book of Records co-founder and conservative political activist Ross McWhirter was assassinated; he had offered a £50,000 reward to anyone willing to inform the security forces of IRA activity.

[2] The four members of what became known as the "Balcombe Street gang", Joe O'Connell, Edward Butler, Harry Duggan and Hugh Doherty, were part of a six-man IRA Active Service Unit (ASU) that also included Brendan Dowd and Liam Quinn.

[5][6] Inspector John Purnell and Sergeant Phil McVeigh, on duty as part of the dragnet operation, picked up the radio call from the team in Mount Street as the stolen Ford Cortina approached their position.

Other officers joined the chase, with the four IRA men running into a block of council flats in Balcombe Street, adjacent to Marylebone station, triggering the six-day standoff.

[9] The four men went to 22b Balcombe Street in Marylebone, taking its two residents, middle-aged married couple John and Sheila Matthews, hostage in their front room.

[12] Despite telling the police that they (The Balcombe ASU) were responsible, they were never charged with these offences and the Guildford Four and Maguire Seven remained in prison for 15 more years, until it was ruled that their convictions were unsafe.