Taking 70 teenagers, a 22-piece band, a large lorry and a full theatre set on a two-week, 560-mile round trip from Shrewsbury to the Edinburgh Festival Fringe may not be everyone’s idea of a good summer break. But Peter Fanning, housemaster at independent Shrewsbury school, loves it. “Physically, it’s exhausting. But spiritually, it’s like a sabbatical to me.”

Mr Fanning first took a school production to the Fringe in 1994; this year is the fifth time he has accepted the challenge. And next Wednesday, under his direction, the school’s production of The Bubble - a musical about the stock exchange shenanigans of 1720s London - will open at Edinburgh’s Southside Theatre. Although it’s competing against 1,500 other shows on the Fringe, Mr Fanning is confident of making a mark. The school’s 1995 production, Jekyll, won a prestigious Fringe First, and The Lost Domain in 2000 made the front page of the Scotsman’s festival supplement, was reviewed enthusiastically by the Observer and the Independent, and played to packed houses.

“We’ve been in the graveyard slot before now. But this year we’ve been offered 8pm - prime-time viewing,” enthuses Mr Fanning. “The average audience on the Fringe is fewer than 20 people. Some shows get no one. But we’ve booked for 10 nights, the most we’ve ever done. I suppose it’s a gamble, but we’re confident.”

The Bubble has an impressive team behind it. Two professional writers have collaborated on the script - Peter Hankin, who teaches part-time at Shrewsbury and who used to write for the BBC’s Play for Today series, and Julian Roach, who has written for Coronation Street for more than 30 years. The songs have been composed by the school’s director of music, John Moore, who has written film scores and is guest conductor at the Bridgnorth festival. And before turning to teaching, Peter Fanning ran his own theatre company.

The school’s first visit to Edinburgh, eight years ago, was with Guys and Dolls, but since then it has been writing its own shows. “It’s more work - just transcribing the orchestra scores takes a week - but it saves on royalties,” says John Moore. “And I can write songs for specific performers. I know their voices and their limitations.”

It was largely Mr Moore’s experience that first got the school to the festival. He had worked in Edinburgh for 10 years and had run various Fringe projects. But accommodating the demands of the school year took a bit of extra planning. External exams make producing a show during the summer term almost impossible, so the hard work is done in the autumn, with each new musical premiered in November in the school’s own theatre.

“It means the show is tried and tested,” says Mr Fanning. “I wouldn’t take something that was completely new. The Bubble was fine in November. And you just know that at the Fringe it’ll be transformed - energy levels will go through the roof.”

Which is a good job, as the cast will tackle everything from 5am dress rehearsals to hard-sell marketing on the Royal Mile. When you’re trying to fill a 250-seat venue for 10 days, a coachload of family and friends only goes so far. So costumed performers take turns to walk the city and sell the show.

Roz Case, a student at Shrewsbury high school for girls and one of several female actors borrowed from local schools, plays a lead role and knows that glowing reviews would help pull the crowds - but that no allowances will be made for age. “You have to work harder, because critics assume it’s going to be ‘a school play’. You have to overcome that. The bottom line is that if you’re no good, no one will come to see you,” she says.

Some of the cast will get a taste for the limelight - previous performers have gone on to roles in London’s West End and with the Royal Shakespeare Company - but for most this will be the pinnacle of their theatrical career.

Peter Fanning is convinced the cast get “a real cultural experience, a once-in-a-lifetime opportunity”. He would recommend it to any school, but with a few words of advice: keep the show simple, don’t have too many expectations and, above all, plan for every eventuality.

“The festival can be a slightly mad experience. There was the time we had our van impounded for being overweight. Our entire set was stuck in a depot on the M6. Another year our tender love songs were drowned out by a transvestite rock cabaret in the adjoining venue. Life on the Fringe is never dull.”

But anyone hankering after this kind of excitement might want to talk to the bursar. “It’s, um, expensive,” admits Peter Fanning. How expensive? “Enormously expensive.” It costs around pound;50,000. The school charges each performer pound;400 towards accommodation expenses. There are sponsorship deals, fund-raising events and ticket sales, but ultimately the whole thing has to be underwritten by the school. “But it’s terrific PR,” points out choreographer Sara Hankin. “In that sense it’s value for money.”

The financial commitment helps explain why the school attempts the Fringe only once every two or three years (and, perhaps, why there are very few school companies on the Fringe programme this year). The other reason is workload - taking 70 pupils to Edinburgh for a fortnight involves a lot of effort. Especially as many of them will receive their GCSE and A-level results while they’re away.

“Just feeding everyone is a challenge,” says Ms Hankin. “We give our order to the take-away a day in advance to make sure it can cope.” The cast and crew are accompanied by at least 10 adults - including some parents - and all stay in university accommodation in the city.

So is it all worth it? Peter Fanning thinks so. “It’s extraordinarily special. Lots of people go to Edinburgh hoping to make it big, then leave with broken hearts and broken pockets. We get the chance to indulge our passion - but then we’ve got the day job to come back to!”

‘The Bubble’ by Shrewsbury school at Southside Theatre Edinburgh, August 14-24, at 8pm. Tickets: pound;6 and pound;8. Box office: 0131 662 0900.Fringe productions by other schools: ‘Six Characters in Search of an Author’ by St Paul’s girls’ school, London, at C Cubed, August 4-10, at 3pm; ‘Oh What a Lovely War’ by Radley College at Augustine’s, August 13-16, at 12.50pm; ‘After the Hole’ by Charterhouse, at Rocket @ South Bridge Resource Centre, August 12-24 at 6.20pm; Eton College (as Double Edge Drama) has three productions, all showing at Edinburgh Central Library from August 5-25. They are ‘Kassandra’ at 2.45pm, ‘The Dumb Waiter’ and ‘Victoria Station’ at 4pm, and ‘Wreck the Airline Barrier’ at 4.40pm