When did Provisional IRA attack 10 Downing Street?

For most of its history, Number 10 was accessible to the public. Early security consisted of two police officers. One stood guard outside the door. The other was stationed inside to open it. Since the door had no keyhole, the inside officer depended upon the lone outside officer.

During Thatcher's premiership, terrorist threats led to the implementation of a second level of security. Guarded gates were added at both ends of the street. Visitors could then be screened before approaching the door.

Despite the added measure, on 7 February 1991 the Provisional IRA used a van they parked in Whitehall to launch a mortar shell at Number 10. It exploded in the back garden, while then prime minister John Major was holding a Cabinet meeting. Major moved to Admiralty House while repairs were completed. This led to the addition of guardhouses at the street ends as well as other less visible measures. Each guardhouse is staffed by several armed police officers. The Metropolitan Police Service's Diplomatic Protection Group (DPG) provides overall protection and acts on intelligence from MI5.