The elderly gent in the corner by the window is soft-spoken and wears a hearing aid. But the people with him - a school governor or two, plus a bigwig from the local education department - are in fits. “I am a one-man designated smoking area,” confides the gent. “I did peel off from a BR train many years ago a label that said ‘Smoking’. I used to stick it on other trains when I get on, and it confused the guard.”

Not that anybody at Ernest Bevin college begrudges Tony Benn a pipe tonight, even if it is against school policy. For in a little over an hour, he and three other politicians will be joining Jonathan Dimbleby (he’s the dapper chap over there, talking with headteacher Naz Bokhari) in an event that will put this south-west London comprehensive on the map.

It is Friday evening, and the school, like many hundreds before it over the past half a century, is about to host Radio 4‘s Any Questions? But this is a special edition of the programme - it falls precisely on the 50th anniversary not only of Ernest Bevin’s resignation as foreign secretary in Clement Attlee’s government, but also of Tony Benn’s first appearance on the programme.

“Hello, hello. Nice to see you.” Mr Benn is with a group of uniformed sixth-formers now, four of the 20 students in their year who will be sitting in the audience as the show goes out live from the school hall.

“And what are you all hoping to do when you leave? Two doctors, a pharmacist and a dentist, eh? My dentist asked me if he could come to the House of Commons, so I got him a special ticket. Next time I go to him I feel sure I will get special treatment. Are you asking questions tonight? No, no, you mustn’t tell me what they are, otherwise I shall start trying to think of answers, and that would ruin it.”

Across the room, Mr Benn’s fellow panellist, the Tory MP Teresa Gorman, is having a similar conversation, while the Lib Dem peer Lord Steel, another Any Questions? veteran, checks his watch and mingles. Fifty minutes to go, and the room, which tonight boasts not only a cold buffet but also a display about the life of Ernest Bevin loaned for the occasion by the TUC and the transport workers’ union, resounds with laughter and the merry clink of glass on bottle. All of which is music to the ears of teacher Barry Jefferson, head of humanities and the man who, for the past few weeks, has been co-ordinating the operation to make the show a success. Has he been looking forward to it, in spite of the extra work involved? “More than a little,” he says, glancing at his watch before darting downstairs to see how the hall is filling up. Forty minutes to go.

It all began in 1997, when Geoffrey Thomas, then head of business studies, spotted a paragraph buried in the school development plan urging staff to think about ways of enhancing awareness of the college in the local community. He wrote to the BBC asking if Ernest Bevin college could host the show, was told that it would be put on the waiting list, and thought little more about it.

Mr Thomas has left teaching now. But he is back tonight, hardly able to believe that, three-and-a-half years later, his brainwave has finally made it to the shore. “I’m pleased with the way things have worked out,” he says. “This school doesn’t have it easy. Not many things really come its way.”

Certainly the Tooting comprehensive will have been up against some stiff competition for tonight’s honour. “At least 70 per cent of applications to host the programme are from schools,” says producer Lisa Jenkinson. “And I’ve become increasingly careful about who I pick. It’s a question of how keen they are. If I look through the folder and see we’ve had three applications from a school in three years, I know they must be keen.”

And when it comes to finding up to 500 people who will turn out to fill a hall at the end of a working week, enthusiasm is essential, particularly for schools in less affluent areas. “Nine times out of 10, the school does the whole thing,” says Ms Jenkinson. “It invites us, does the organising and sees it right through. And while a school in a middle-class area can rustle up 500 people with no trouble, some inner-city schools can find it difficult.”

But, for the right school, hosting Any Questions? is usually a rewarding experience. “A lot of the students like it,” says Ms Jenkinson, noting with relief that tonight’s remaining panellist, the Tory veteran Michael Heseltine, has just arrived. “The way they get involved can be quite astounding. We run on a small budget, so we pay pound;50 towards the cost of the hall, and we say that if they would like to put on a small buffet and meet the panel afterwards, that would be fine. They seem to enjoy it and we love it, so it all goes very well.”

While the programme goes out from all sorts of venues, including churches, museums, universities and village halls, it makes sense to include a high proportion of schools among the venues, says executive producer Peter Griffiths. A school will be able to assemble a range of generations in the audience. And on a special occasion such as this, a school that is an integral part of the community can offer something extra in terms of an appropriate setting.

“For this programme, we chose a school in a mixed community rather than a posh museum or a church because we wanted to put Tony Benn back on the hustings, in a place where he would feel he was working as a politician,” says Mr Griffiths.

“Once a school has been chosen, it must nominate an organiser and set up a working party. We send out a briefing to each school we select, guiding them as to the kind of help we really need and the kind of standard to be set in terms of organisation. The rest is their enthusiasm and hard work.”

Ernest Bevin college has been “exemplary”, he adds. And in less than half an hour all the time and effort will bear fruit.

Far from struggling to fill the hall, Barry Jefferson has had his work cut out ensuring that the 350 free tickets for tonight’s broadcast are distributed fairly.

“I’ve used some boys in Year 10 for leafleting,” he explains. “And the local papers have been running a competition for some tickets, which has been good. The school is 80 per cent non-white, so we have tried to reflect that. We gave equal numbers of tickets to each of the three main parties - 20 for Labour, 20 for the Liberals and 20 for the Tories. The primary schools have also been very interested, so we have given tickets to our six or seven main feeder schools.”

Then there were governors and local authority officials to consider, to say nothing of parents, staff, pupils and former pupils. “Local residents have been keen. People keep phoning me to get tickets, but I’ve run out.”

The BBC usually asks that a school provide seating for between 200 and 500 people, as well as an adequate BT line so the programme can be relayed to the transmitters. “After that, they do it all for you on the technical side,” says Mr Jefferson.

“They provide posters on which you just fill in dates and the names of the panel. Then, on the night, they bring a box for the audience to put their questions in as they arrive. A room must be provided for the reception, and another room where the questions can be filtered. And, on the day, they turn up with a van and put the whole thing together.”

Not that “van” adequately describes the big Mercedes with an equally big trailer that pitched camp like some travelling circus at Ernest Bevin College this afternoon and disgorged drums of cable and rolls of tape, and as many control panels, speakers, mikes, lights and electronic bits and pieces as could be crammed into the two vehicles.

Banners and drapes were also in the cargo, and these have transformed the school hall into something resembling the venue for an annual party conference.

On the platform, crisp turquoise tables bear the BBC Any Questions? logo and, standing alone in their midst with just a quarter of an hour to go, Lisa Jenkinson addresses the audience. Those whose questions have been selected will sit in the front two rows. Here are their names and numbers. Where is question six? “He’s gone to the loo,” says a voice from the back, to general applause. The crowd is warming up nicely.

“It’s important that you join in,” says Ms Jenkinson. “Our panellists always tell us they would rather have a negative response than no response at all. The microphone will not pick up individual comments, just a general murmur. But you can clap and you can boo, and that will get your feelings across.”

There is a round of applause for Barry Jefferson, “who has put in a lot of hard work”, and he arrives in the hall looking bemused, just as the clapping is dying down. But before he has time to pick himself up, the platform is full of famous faces.

“I shall start the programme in five minutes from now,” says Jonathan Dimbleby as a hush falls over the proceedings. “But first of all the sound engineers need to listen to the panel, and we do that exercise by means of a warm-up question.”

With two minutes to go, he pours water from a jug to demonstrate to the panellists how such actions, carelessly performed, can easily result in disconcerting gurgles for the listeners at home. And then, as the laughter subsides, the 8 o’clock news - the real-time Radio 4 bulletin that always precedes Any Questions? - comes as if by sorcery through the speakers in the school hall. Seconds later, Mr Dimbleby is introducing the programme, the panel, the school.

“Welcome to south-west london,” he says, “where we are in Tooting at the Ernest Bevin college, an all-boys’ comprehensive which among other accolades has just won the Schools Curriculum Award 2000. We’re here on the 50th anniversary to the day ofI” But the rest is history - broadcasting history, Tooting social history perhaps and, without question, school history.

“Absolutely brilliant,” says the beaming head, three-quarters of an hour later as the final round of applause begins to fade. Even schoolkeeper Phillip Nelson is looking cheerful after watching the show from the back of the hall. Mr Nelson and his colleagues have 350 clanking metal chairs to stack away before they can call it a night. But, as he bangs and stacks, he has a big grin on his face.

“That Tony Benn - I liked his speech a lot,” he says. “Very entertaining.”