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Special Branch is a label customarily used to identify units responsible for matters of national security in British and Commonwealth police forces, as well as in Ireland's Garda Síochána. A Special Branch unit acquires and develops intelligence, usually of a political nature, and conducts investigations to protect the State from perceived threats of subversion -- particularly, terrorism and other extremist activity.

The first Special Branch, or Special Irish Branch, as it was known, was a unit of London's Metropolitan Police formed in March 1883 to combat the Irish Republican Brotherhood. The Irish soubriquet was subsequently dropped as the unit's remit widened.

Colin Lamb worked closely with them at the conclusion of the story The Clocks.