One terrible moment 17 years ago changed political party conferences for ever in Britain.

It was when an IRA bomb blew apart the Grand Hotel in Brighton killing five people, maiming many more and narrowly missing the Prime Minister.

With typical resolution, Margaret Thatcher declared the show must go on and it did even though there was death and destruction nearby and many blast victims had to wear clothes borrowed from Marks and Spencer.

But that terrorist outrage ended the carefree nature of conferences and ensured that security would always be a prime consideration.

Now we have another terrorist threat before us.

The Tory conference in October has already been shortened and Labour's visit to Brighton next week will also be curtailed.

Only the Liberal Democrats have limped through the full length of their conference at Bournemouth and even that has been a low-key, mournful affair conducted in the shadow of the World Trade Centre wreckage.

We shouldn't give in to the terrorists and should try to carry on with our normal way of life which is why conferences have continued at huge expense to the taxpayer ever since.

But there is a real question mark over whether conferences are worthwhile because of other changes during the last 20 years which have nothing to do with terrorism.

For many years the Tories, who were the natural party of government for most years after the Second World War, conducted their conference, not as a forum for democratic discussion, but as a strategy showpiece for cabinet ministers and the Premier to make announcements.

Gradually Labour, and even the anarchic Liberal Democrats, have followed their lead.

There were great battles and moments of history at Labour conferences in the past. It was at Brighton that Denis Healey defeated Tony Benn in 1981 for the deputy leadership by the narrowest possible margin, preventing a fissure which would probably have split Labour in half.

Two years later, Neil Kinnock was chosen as leader and started Labour's long haul back to electability.

Nye Bevan memorably told a Labour conference debating the nuclear bomb that he would not go naked into the conference chamber. Hugh Gaitskell said he would fight, fight and fight again for the party he loved. Harold Wilson declared in the soaraway Sixties that the way forward was through the white heat of the technological revolution.

There have been a few magic moments at party conferences since those days. Margaret Thatcher told doubtful Tory representatives in Brighton worried that she might do a U turn on policies: "You turn if you want to - the lady's not for turning." Neil Kinnock stood up to Militant when that faction was gnawing deep into the party's organs. David Steel prematurely told Liberals to go back to their constituencies and prepare for government.

But there is little genuine debate these days and few decisions of importance are taken at party conferences. Increasingly they are glitzy occasions, aimed at the media in general and TV in particular. Behind the scenes, there are few smoke-filled rooms with people plotting revolutions over beer and sandwiches but rather elegant soirees where delegates sip fine wines at the expense of companies hoping to court them.

The leaders' speeches, always far too long and flatulent, are often not in their own words. Even Margaret Thatcher's U turn soundbite was written by the playwright Sir Ronald Millar and not by her. Tony Blair has the actor's knack of sounding sincere but there is a mighty machine behind him producing many of his lines.

Who are conferences for? Not the delegates who increasingly feel powerless and passed by during their proceedings. Not the media who have to put up with a lot of public relations fluff and find few stories of note. Not the politicians themselves who prance around on stage mouthing platitudes.

It was the right decision this year to carry on with the conferences, however truncated. But in the future, all three major parties should seriously consider whether their autumn shindigs by the sea are really worth holding any more.

Cancelling them would be Brighton's loss but Britain's gain.