Since 1989 , entering Downing Street has required passing through a security checkpoint . The street is patrolled by armed police from the Diplomatic Protection Group , and there is usually at least one police officer outside the front door of Number 10 . Security was tightened after 10 Downing Street was mortar bombed by the IRA in 1991
mortar bombed by the IRA in 1991
Downing Street mortar attack
Downing Street