The Provisional Irish Republican Army bomb the British Houses of Parliament on June 17, 1974, causing extensive damage and injuring eleven people.

The Provisional IRA begins a bombing campaign in England in March 1973 when they bomb the Old Bailey courthouse, injuring over two hundred people. The following year is the worst year of the Troubles outside of Northern Ireland. At the beginning of 1974, the IRA explodes a bomb on a coach carrying soldiers and some family members on the M62, killing twelve people, including four civilians. A month before the Houses of Parliament bombing, thirty-four people are killed in the Republic of Ireland in the Dublin and Monaghan bombings of May 1974 carried out by the Ulster Volunteer Force, an Ulster loyalist paramilitary group based in Northern Ireland, the worst single incident of the conflict.

A man with an Irish accent telephones the Press Association with a warning given just six minutes before the device explodes. London police say a recognised IRA codeword is given. The bomb explodes in a corner of Westminster Hall at about 8:30 a.m. on June 17, 1974. The IRA in a telephoned warning says it planted the bomb that weighed approximately 20 lbs. (9.1 kg). The explosion is suspected to have damaged a gas main and a fire spreads quickly through the centuries-old hall in one of Britain’s most security-tight buildings. An annex housing a canteen and a number of offices is destroyed, but the great hall itself receives only light damage. The attack signals the start of a renewed IRA bombing campaign in England that is to last until late 1975 and is to claim the lives of dozens of people. The most notorious attacks of the bombing campaign are the Guildford pub bombings on October 5, 1974, that kill five and injure sixty, and the Birmingham pub bombings on November 21, 1974, which kill twenty-one people and injured one hundred eighty.

The year 1974 ends with the IRA killing twenty-eight people (twenty-three civilians and five British soldiers) in bombing operations in England. Twenty-one people are killed in the Birmingham pub bombings and a further seven are killed in the Guildford and Woolwich Pub bombings. Nearly three hundred people are injured from these bombings alone. The IRA calls off their bombing campaign in February 1975 but restarts it on August 27, 1975, with the Caterham Arms pub bombing which injures over thirty people. A week later, the IRA carries out the London Hilton bombing which kills two and injures over sixty.