In 2008, a student theatre company came out of nowhere and stunned the Fringe. A no-name group from York, making their Edinburgh debut, surprised everyone with a four-play suite which included adaptations of works by Ben Jonson and Euripides. They secured some critical and popular acclaim, and must have been thoroughly pleased with themselves. But then they clinched the first-ever Edinburgh International Festival Fringe Award, and with it an invitation to come back and make an appearance the following year at the Fringe’s well-heeled big brother, EIF. All of a sudden, things had become very interesting for Belt Up Theatre...

Five years later, and Belt Up’s star is still in the ascendant. The last two years have been especially kind to them: their intimately-staged interactive tales of lost childhood — The Boy James, inspired by the life and work of JM Barrie, and Outland, by Lewis Carroll — met with widespread acclaim, and opened the door for the company to tour the pieces across the UK and internationally, including a successful run at the Adelaide Fringe in February. From an upstart student group doing clever takes on classic theatre, Belt Up are suddenly a household name among those ‘in the know’, and even more dubious observers — The Guardian’s Lyn Gardner chief among them — seem to view them as a highly promising proposition.

But when I join co-founders and artistic directors Jethro Compton and Dominic Allen for coffee at Edinburgh’s tourist-chic Elephant House, a week before the start of their fifth Fringe run, there are few airs and graces. These are not young thespian rockstars holding court; in fact, the sense you get from them is a mixture of excitement — joie de vivre, almost — and fierce, single-minded focus. That’s probably for the best: there isn’t time for self-congratulation, because in less than a week Compton and Allen will be doing three shows a night.

When you sit them side-by-side, the pair resemble a finely-honed double act. Compton is cheerfully energetic: holding forth eloquently, he gesticulates forcefully, and his eyes dart around the room — to his partner, to their PR man sitting quietly at the end of the table, and back to his interrogator. Allen is quieter; more introspective. Slightly pale, bespectacled and bearded, he speaks softly — he’s witty and articulate, but less overtly theatrical than his colleague.

Belt Up’s outlandish work ethic might have had something to do with their success. In the last four years, Belt Up have performed 17 shows at the Fringe — including a superhuman eight in 2010 alone. After this year, that total rises to 20. Belt Up have brought three shows to this year’s festival — audience favourites The Boy James and Outland, and new play A Little Princess — and are doing full runs of each in the same space, from 6:30pm to nearly midnight. And as if that wasn’t enough of a physical, psychological and logistical challenge, the same small cast is used for all three shows: Compton and Allen, plus longtime ensemble member Serena Manteghi. Asked about their personal preparations, Allen is quick off the mark.

“Berocca,” he quips.

“Vodka,” offers Compton. They play coy when asked if they’ve ever done The Boy James drunk; eventually their PR steps in with a mock-horrified cry of “Don’t answer that!”

“The shows are very balanced,” says Allen, serious now. “So we are the respective lead in each... So we know which show is going to kill us.”

Later, reflecting on the month ahead, Compton professes they’ve been cautious. “I allowed a lot of contingency time. Because this [set] build was so ambitious, and we had no idea how it was going to go, because we’re in a new venue... there are lots of unknowns. But also, we are busy making one new show, and trying to make it as good as possible, as opposed to trying to do ten shows with 21 people. That’s the big difference — that we're sleeping, whereas in 2010 I was running on about two, three hours of sleep a night for the whole of July. When we’re saying ‘sustainable’, it’s not just finance, it’s also health...

“We don’t have time to die.”

Compton and Allen, with their co-directors Alexander Wright and James Wilkes, founded Belt Up in 2008, while studying at the University of York. They made their name with inventive adaptations of Kafka and Molière texts, but with graduation looming and the real world beckoning, Belt Up’s future was far from certain.

Providence intervened. In mid-2009, they were invited to become the resident company at York’s Theatre Royal, ranked among the UK’s leading regional theatres. “We’d literally just come back from the 2009 Fringe,” recalls Allen. “And we had a coffee with Damian Cruden, the artistic director, to potentially talk about maybe doing something in the studio at some point.

“And he said, ‘oh, you can have a residency. We’ve got a spare office upstairs.’ It was all very surreal.”

It was a fortuitous twist in the Belt Up story, says Allen. “It was a point where we didn’t really know what to do next... We were working out of our bedrooms.

“It lacks a certain class.”

“There was a support network within [the residency],” chimes in Compton. “You’re on the internal phones, and with three numbers you’re speaking to the people who are running one of the best producing regional theatres in the country, saying ‘I think we just fucked something up.’ And they will tell you, ‘Yes, you just fucked that up.’ So that was fantastic.”

That incubation; the freedom to learn from experienced professionals, seems to have marked a turning point for the company. But it was The Boy James that pushed the Belt Up brand to national prominence. The show — a claustrophobic, surprisingly dark bildungsroman which blends inflections of Peter Pan and Barrie biography — was “a secret success”, says Compton, “because we didn’t expect it to do as well as it did.

“Not for a qualitative reason,” he is quick to add. “But just because we had some shows were smaller shows, that were on every other day, and they were just there for a bit of fun... and they were just little projects that people wanted to do. So Alex [Wright] had written this play, and really wanted to put it on.”

Success in Edinburgh led to a three-week run at the Southwark Playhouse in London; a deal done “on a handshake” with the theatre’s artistic director Chris Smyrnios after another show pulled out. The Boy James continued to gather momentum — “Stephen Fry came to see it,” Compton name-drops, breezily. (Apparently the humourist was impressed: “Just been knocked out by "The Boy James" Belt Up's interactive show about J. M. Barrie at The Southwark Playhouse,” he tweeted. “Still drying my eyes.”)

The Boy James’ surprise ascendancy as Belt Up’s flagship production altered the company’s perspective. “That kind of shifted what we wanted to do, in a way,” says Allen. “We’d sort of felt that what people wanted were our Kafkas and our big, ensemble shows,” Compton adds, “and whilst those are brilliantly fun to do and do get a good response, they’re incredibly hard to sustain.

"You can’t take our production of Metamorphosis around the world the way you can take these shows.”

Suddenly Compton and Allen are talking about business models and financial sustainability: our conversation has turned to the practicalities of running a theatre company in 2012, and of the struggle to achieve the company’s creative goals at the same time.

As we talk about the then and now, there’s an interesting parallel with the lost-innocence theme so prominent in Belt Up’s recent work; something faintly Peter Pan-esque about their professional trajectory. As the founders graduated and were forced to confront the realities of life outside university, so too was Belt Up as a company forced to adapt and undergo the same process of maturation. Both remain ambitious and idealistic, but listening to Compton and Allen discuss logistics, the men’s optimism and clear devotion to their art seems tempered by faint sadness about the compromises that they have had to make and the challenges of trying to run a theatre company in an age where funding for the arts dwindles by the year. The company’s touring cast, for example, is much reduced from their days as a student company: in 2009, there were twelve actors; now, there are three, because they aren’t students anymore and people need to be paid.

“We’ve had Edinburghs where we’ve had 21 people performing,” says Compton, “and it’s a lot of fun. Every night’s a party. But what we’re having to do is transition from being a student company, when everyone was working for free, and now that we’re a professional company everyone has to get paid. Bringing 21 people to the Fringe is not sustainable.

“It’s about making sure that the shows can have a future, and that they don’t become too expensive to do.”

And yet Compton, who is also a professional producer, is remarkably upbeat. "That's one of the things I really enjoy about it — the business side of showbusiness. It's finding a way to maintain artistic principles, and everyone getting paid, and not letting the company fail."

Indeed, Belt Up was necessarily born with a live-or-die business mentality. As Allen points out, the company came into being in a time of recession and crisis for arts funding. "We've never been state funded. We missed out on the golden age of the Labour government, so we were there at the tail end, when it was getting harder to get money."

But they seem to be adapting to the strictures of life as professional thespians. 2012 marks the premiere of A Little Princess, which completes a trilogy (along with Outland and The Boy James) of shows focusing on the idea of childhood — and particularly its loss. The shows share something not just in theme but in execution: “the way [they] work is you have a young guy, a young girl and an old guy,” says Compton. Then, gesturing at Allen. “Or an older-looking guy, because he has a beard.”

The Boy James focused on the boy, and Outland on the man. Now, with A Little Princess, Belt Up are bringing the girl out of the shadows, and putting her centre stage. "We were in Australia, and we were trying to work out what would work [to complete the trilogy]," says Compton. "And the idea of A Little Princess was brought up." Like its forerunners, Belt Up's A Little Princess has literary origins: it’s an adaptation, with biographical tangents, of Frances Hodgson Burnett’s novel of the same name. "It is A Little Princess, you get the whole story... but it is very much our adaptation of it. So it brings in other stories by the author, and other elements of the author's life are also interweaved."

A little later, Compton and Allen stride onto the elaborate — and, our photographer is gently warned, top-secret — set the company have built inside C nova. The space, which will be used for all three shows, is a eclectic home-away-from-home; a cozy, unorthodox auditorium with something oddly foreboding about it. As we arrive, Manteghi is perched on a chaise longue sewing costumes, while A Little Princess’ director, Joe Hufton, bustles around overseeing final preparations. The four banter and laugh; Compton explains his new-found love of nailguns, and Manteghi looks worried. It's discovered that some furniture loaned by a friend was illicitly varnished, and everyone looks worried. They trade war-stories of past shows, howling with laughter at private, you-had-to-be-there jokes. There’s something intriguingly DIY about the whole production, and a familial dynamic among the group — and then, in that moment, away from all talk of bottom-lines or break-down times, Belt Up are right back to having fun in what they do.