During the Troubles , as part of its armed campaign against British rule in Northern Ireland , the Provisional IRA had repeatedly used homemade mortars against targets in Northern Ireland . The most notable attack was the 1985 Newry mortar attack which killed nine members of the Royal Ulster Constabulary . The IRA had carried out many attacks in England , but had not used mortars there . In December 1988 items used in their construction and technical details regarding the weapon 's trajectory were found during a raid in Battersea , South London by members of the Metropolitan Police Anti-Terrorist Branch . In the late 1980s , British Prime Minister Margaret Thatcher was top of the IRA 's list for assassination , following the failed attempt on her life in the Brighton hotel bombing . Security around Downing Street had been stepped up at a cost of £ 800,000 following increased IRA activity in England in 1988 , including the addition of a police guard post and security gates at the end of the street . Plans to leave a car bomb on a street near Downing Street and detonate it by remote control as Thatcher 's official car was driving by had been ruled out by the IRA 's Army Council owing to the likelihood of civilian casualties , which some Army Council members argued would have been politically counter-productive
Brighton hotel bombing
Brighton hotel bombing
Downing Street mortar attack