This year's Labour conference in Brighton comes 20 years after IRA bombed the Tory gathering in the resort.
By Ollie Stone-Lee
BBC News Online politics staff
BBC News Online looks at how the Brighton bomb changed party conferences and how memories are being stirred by the anniversary.
The hotel chimney collapsed through the middle of the building
Just how close the British government came to extinction will be weighing on the mind of Michael Brown this week as he walks past the scene of the Brighton bomb blast.
Mr Brown is one of the few people attending Labour's gathering this year who was an MP at the ill-fated 1984 Conservative conference.
Now a commentator for the Independent newspaper, Mr Brown says he will be silently thinking about the bomb this week in Brighton.
The bomb was planted by top IRA bomber Patrick Magee 24 days before the blast behind a bath in a sixth floor room at the Grand Hotel which was never searched.
It killed five people, injured 34 others and nearly wiped out most of Margaret Thatcher's Cabinet.
Ex-MP Mr Brown will be especially be thinking of Anthony Berry, the one Tory MP killed in the blast and to whom he was quite close.
"To be honest, every time I've been to Brighton to party conferences subsequently I have spared a thought about it."
On the night of the bomb, Mr Brown bumped into Mr Berry at about 11pm and two MPs walked their four dogs together along the beach.
"I never saw him again," says Mr Brown, who was staying about a quarter of a mile from the Grand Hotel.
He had been allowed to smuggle his two King Charles Spaniels into his hotel room on condition they made no noise.
Mr Brown did not hear the bomb but did wake up soon afterwards.
"My dogs were suddenly barking the place down in the middle of the night," he says, who first reaction was to worry his dogs would be confiscated for waking up the neighbours.
The blue flashing lights down the seafront signalled there was something amiss but in the days before satellite television, it was not until the next morning's broadcasting he discovered the full story.
There was complete shock and horror as the conference continued as normal while search teams sifted through the hotel rubble.
Magee set the bomb to explode 24 days later
"If a room had been chosen slightly differently for the bomb, we could have been looking at the whole of the government being wiped out. It made us all shiver and run cold."
Mr Brown says the bomb changed everything, as the ring-of-steel round Labour's conference venue this year will show.
"MPs, journalists and delegates used to pride themselves that conference was the one occasion where with reasonable ease anybody could button hole senior politicians," he says.
'Wake up call'
He fears security now has got away from the determination to ensure normal life continues as much as possible, although accepts the government is acting on advice.
Sussex Police is putting on its biggest ever operation to secure the conference island this year, although says there is no specific information about a threat.
More than 1,000 police are taking part in Operation Otter, with pontoon shaped barriers made of steel and encased in concrete being positioned around the sealed site.
Policing will be tight in Brighton
Security analyst, and former counter-terrorism officer Charles Shoebridge says the Brighton bombing was a "wake-up call" for the British police as far as the mainland was concerned.
"The meticulous IRA planning and preparation involved, and the relative sophistication of the device itself, had been largely unexpected," he says.
Mr Shoebridge says the lessons of Brighton have fed into the methods now used to secure conference venues.
Good detective and intelligence work led to the capture of Patrick Magee, he says.
"Twenty years later, this still forms the basis of successful counter-terrorism operations," he adds.
"However, even today, the bombing itself is seen as a lesson in how a lack of thoroughness and imagination and, above all, an under-estimation of a terrorist threat, can have disastrous consequences."
Crispin Black, a director of the Risk Advisory Group, says security at the 1984 Tory conference was comprehensive and severe, despite being low key by post-11 September standards.
"It would have been almost impossible to shoot Mrs Thatcher or introduce a bomb inside the cordon once the area had been secured," said Mr Black, an intelligence expert who has worked for the Army and the Cabinet Office.
"But the Provisionals got through thanks to a recent technical innovation - imaginatively used.
"The acquisition by the IRA of electronic timers which could be set up to 28 days in advance (quite something in that pre-computer age) meant that a bomb could be introduced into the hotel before the security cordon was in place - and then detonated automatically without any further human involvement."
Mr Black says the bomb led to record keeping being improved - not least because Magee was identified through his entry in the hotel register.
But he adds: "The most important effect of the Brighton Bomb was to make the security forces realise that in some circumstances they had to secure areas in four dimensions rather than three - the time an area became secure became important.
"This was most clearly seen at the Athens Olympics where the main stadia and other crucial facilities were "locked down" months before the beginning of the games."
This month's invasion of Parliament by pro-hunt protesters and the Fathers 4 Justice demonstration at Buckingham Palace have prompted a new appeal from Sussex Police Chief Constable Ken Jones.
"I ask those intent on publicity stunts, civil disobedience or worse to stay away from Brighton and let my officers concentrate on the real threats we currently face," Mr Jones has said.
Twenty years on from the bombing, the dilemma of how to balance democracy and security lives on in Brighton.