The IRA carried out its most audacious attack on this day in 1984 - bombing the Grand Hotel in Brighton in an attempt to wipe out Margaret Thatcher and her government.

The IRA hatched its plan to assassinate Prime Minister Margaret Thatcher – who they blamed for the death of hunger strikers including Bobby Sands – in 1983. The terrorist group chose the following year’s Conservative party conference in Brighton and the town’s Grand Hotel, as the location – and chose explosives officer Patrick Magee as the man to plant the bomb.

The plan was to use a bomb with a very long delay – and so three weeks before the conference, Magee and a female accomplice checked into the Grand Hotel for four nights under a false name. They stayed in room 629 – five floors above the hotel’s VIP suites – and Magee planted the 20lb gelignite bomb (which used a timer from a VCR) behind the bath panel in the bathroom. He programmed the device to detonate 24 days later, at 02:53am on the last night of the Conservative party conference.

The Tory party conference was a great success – and on the final night, Thatcher stayed up past midnight in her first-floor VIP suite, working on the speech she would be giving to the conference the following day.

Margaret Thatcher and husband Denis leave the Grand Hotel following the bombing.

The bomb exploded at its planned time, when most of the hotel’s 318 guests were asleep in bed. Thatcher, however, had still been up in her sitting room, working with her private secretary, just moments before. “Both she and I knew immediately that it was a bomb,” he later said.

The explosion ripped through the top floors of the hotel, creating a huge hole in its front and causing a chimney stack to collapse and crash through the centre of the building. It missed Thatcher’s living room by inches, but hit her bathroom and bedroom, where her husband Dennis was sleeping.

[Read more: April 24, 1993 - IRA’s Bishopsgate bomb devastates the heart of the City of London]

Many guests and delegates – including cabinet minister Norman Tebbit and his wife Margaret – were trapped by falling masonry and rubble as the rooms collapsed in the centre of the hotel. There were chaotic scenes as wounded survivors made their way out, covered in dust – but fire officers were at the scene by 3am. Margaret and Denis Thatcher were rushed out of the rear of the hotel and taken by car to Brighton police station.

It wasn’t until the following morning that it became clear that several people had died in the explosion and more than 30 had been severely injured – including Tebbit and his wife.

Margaret Thatcher, flanked by William Whitelaw and Douglas Hurd, stands in prayer at the start of the conference's final day.

Margaret Thatcher insisted that the conference would continue as scheduled that day – and as she made her way to the conference centre, the IRA issued a statement taking responsibility for the bomb. “Today, we were unlucky. But remember, we only have to be lucky once; you will have to be lucky always,” it warned. “Give Ireland peace and there will be no war.”

The Prime Minister went against police wishes and entered the conference centre by its front entrance in full glare of the media and gave a redrafted speech to the conference. “The fact that we are gathered here now – shocked, but composed, and determined – is a sign that not only this attack has failed, but that all attempts to destroy democracy by terrorism will fail,” she said, defiantly.