But on this dreary autumn morning, Stormont, home of the new Northern Ireland assembly, does have some visitors. They may not be Nobel Prize winners or British government ministers, but their presence is significant none the less.

Neill Morton, head of political studies at Campbell College - a prestigious boys’ independent school in Belfast - once banned discussion of “domestic” politics in the classroom. “In the past I would have avoided it like the plague,” he says. “Attitudes were so entrenched it was not progressive even to have discussions.”

But here he is with a group of sixth-formers at Stormont to debate the future of Northern Ireland with two politicians: former terrorist David Ervine of the Progressive Unionist Party (PUP), and Bairbre de Brun of Sinn Fein. “These people will be shaping the kind of country the boys will be growing up in,” says Mr Morton. “It’s very important that they have an opportunity to discuss their future.”

The Campbell boys - overwhelmingly Protestant and middle class - would not normally encounter either these politicians or the constituents they represent. Bairbre de Brun speaks for a tough west Belfast republican constituency; David Ervine served five years in Long Kesh in the Seventies for possession of a bomb. He now speaks for the PUP, which has links with the hardline Ulster Volunteer Force paramilitaries.

In the Stormont lobby, the 15 pupils empty their pockets of keys to pass through the metal detector, looking ill at ease. In an upstairs meeting room, sitting at a huge table, Bairbre de Brun begins by telling them that the challenge of the new assembly is “not to reduce difference but to 1ive with difference, accept the continuation of difference and learn to work with difference”. She speaks thoughtfully and convincingly, with none of the defensive posturing associated with Westminster politicians.

Sounding like the teacher she once was, she tells the boys they could be at “the leading edge of creating a new society’’, and cites the example of South Africa. “They have managed to take from the very best of new ideas about how to organise society. We have the opportunity to do the same here,” she says.

In fact, this meeting already represents a new way of organising things. A few months ago the idea of Sinn Fein and the PUP sharing a platform of any kind would have been unthinkable. And Campbell pupils would not have had the stomach for such a meeting. “Their response would have been utterly emotional and closed,” says Mr Morton. “The big difference is that now they’re prepared to listen more closely to other points of view.”

David Ervine, stocky and moustached, has an ebullient style. “No question is that naive that it can’t be asked, and no question is that difficult that we can’t deal with it,” he says cheerfully. “Do not leave here wishing you had asked something that you didn’t ask.’’ He needn’t have worried, as the Campbellians are an articulate lot with plenty of the confidence that their kind of school instills.

The first question is on decommissioning, currently the largest rock on the path to peace. Andrew Bogle, 16 - echoing the position David Trimble, Northern Ireland’s new First Minister, was that day putting in Downing Street - asks if Sinn Fein should be allowed to take up seats in the new assembly before beginning the process of getting rid of their weapons. Bairbre de Brun replies that the Good Friday Agreement “could never have happened if it had included a date for decommissioning”. David Ervine agrees that, as no date was set in the Good Friday Agreement (the paramilitaries are required merely to co-operate with the decommissioning body), Trimble is “on shaky ground” with his demands that a date now be set.

“For me, decommissioning is not deliverable at this time,” says Mr Ervine.“The circumstances of our new future are too juvenile.” A 30-year paramilitary sub-culture cannot be dissolved overnight, he adds. “It’s too simplistic to say that, if you bad guys would just decommission, everything would be all right.”

Mr Ervine and Ms de Brun supposedly stand on opposite sides of the sectarian divide, but here, being held to account by a younger generation, more seems to unite than divide them. “Some day you will have to struggle with the things that we have struggled with,” says David Ervine. “We didn’t all wake up one day in 1969 and decide to be bad people.”

The gap is not just generational, however. Both Mr Ervine and Ms de Brun speak on behalf of working-class constituencies, and here they are addressing pupils from a school indelibly associated with the scions of the ruling class. “I don’t want to upset you, but there weren’t too many middle-class guys in Long Kesh,” says Mr Ervine at one point.

Ervine, who himself benefited from a 50 per cent remission scheme 20 years ago, speaks with a note of irritation. “They couldn’t put us together in schools, they wouldn’t integrate our streets, but they tried to put us in prison together where we could kill each other. It’s all very well to sit in leafy land and cast judgments,” he says. Education is overdue for reform, he adds, as most Ulster schools are still segregated and selective.

The boys are getting more confident. “How can you go to an electorate representing murderers?” asks one, although, with the largest army corps in the six counties, Campbell College is hardly a hotbed of pacificism.

It releases more tension, like slackening a valve on a tyre. David Ervine,the diehard unionist, speaks with a startling passion about the injustices inflicted by the British on the nationalists. “We are an unwholesome society. Get your history books out and then tell me if you think they’re worthy and good and right,” he says. Bairbre de Brun, still speaking as if to a respected friend, says the time is right for everyone to look at their own conscience. “My community does not view all those who were on the legal side as being good and standing up for right.”

David Ervine is evasive when asked how much influence politicians have over the paramilitaries. “We have as much influence as they allow us,” he says. Bairbre de Brun says: “We have influence, but it’s not unlimited. We have positions of respect within our communities, but it’s precisely because they know that we’re treating them honestly,” The politicians do the same with the boys for two hours, talking to them without condescension or impatience. In the steamy minibus on the way back to school the pupils are impressed. “They spoke very reasonably. They seemed eager to get us on side,” says Andrew Adams, 16. Only one boy refused to contribute to the meeting. “I wouldn’t talk to them because they support paramilitary groups that use violence,” says 18-year-old John McCourt.

Neill Morton wasn’t expecting Damascene conversions among his pupils, but he seems to have achieved his aim of “undemonising” the speakers and the organisations they represent. He has no plans for an immediate debriefing. “I want them to regard themselves as independent, adult types rather than students going along with their teacher, and writing up the answers afterwards.”

He is teaching them to think - and talk - for themselves. It’s all the rage in Northern Ireland these days.