IT SEEMS fitting that John Durnin's final show as artistic director of Pitlochry Festival Theatre is Singin' in the Rain. It was Durnin, after all, who first introduced the idea of producing what is a now annual large-scale Christmas show in a theatre which previously focused solely on its summer rep season of plays. During his 15-year tenure in charge of the "theatre in the hills", Durnin has expanded the season into winter even further, with a new staging of The Monarch of the Glen by Peter Arnott being a runaway success this year.

In the summer season of plays itself, Durnin has slowly but surely nudged away perceptions of PFT as an old-school purveyor of conservative commercial staples. On the one hand, he has introduced a stand of contemporary Scottish work by writers such as Liz Lochhead, David Greig and Stephen Greenhorn into the repertoire in ways that at one time would have been unthinkable. Durnin has also staged revivals of neglected 20th century classics such as Peter Barnes' play, The Ruling Class.

At the other end of the scale, Durnin has introduced what has become another new tradition, with PFT's summer season now opening with a big musical. As the show effectively introduces audiences to an ensemble cast they'll get to know well in different guises over the next six months, classics such as Kiss Me Kate and A Little Night Music have been staged with an ambition and confidence rarely seen outside the West End and commercial touring circuit. The success of Singin' in the Rain is a case in point.

“When we first started doing winter musicals in 2012, we knew we were eventually going to run out of festive based shows,” says Durnin. “Leslie Bricuse's musical of Scrooge last year was the last roll of the dice on that. I've long wanted to do Singin' in the Rain, but with all the rain onstage, there was no way we could do it as part of the summer programme. Doing it at this time of year was a bit of a risk as well, because it's not Christmas-based. But what became clear from the moment the tickets went on sale that this title meant a lot to people. Through that, we're seeing the fruits of many years' labour developing that strand now, and in future years whoever's at PFT can look at that and see the very large audiences that came along.”

With such a slow-burning reinvention of a theatre company that began its life in a tent set up by John Stewart in 1951, and which since its current building opened in 1981 has grown to become a major tourist attraction with increasing artistic credibility, why leave now?

“I think every artistic director has a shelf life,” says an ebullient Durnin. “There's no way round that. After 15 years in Pitlochry, I have to think, have I achieved everything I wanted to do when I came here, or have we reached a kind of plateau phase? If so, then it's time for fresh challenges. PFT has come an incredibly long way since I arrived here. When I came to Pitlochry in 2003, it was a summer repertoire and a more conservative programme. Since then, we've become a year-round operation, and our range of plays is much broader.

“Having gone on this incredible journey and seen these various ambitions ticked off one by one, with PFT now much better regarded in Scotland, the UK and abroad than it was before, it feels very much like mission accomplished.”

Despite his achievements in Pitlochry, there are things that haven't worked out. Durnin takes a frank and philosophical approach to such short-comings.

“Of course, there are always going to be regrets doing a job like this,” he says, “and if we'd had more time then we might have achieved other things. I'd hoped we might have developed new work more. I'd also hoped we'd have been able to re-introduce Shakespeare and Shakespeare's contemporaries into the repertoire, but given everything we have done at PFT in the last 15 years, I can't be disappointed. And I think there's now a great platform for a new creative intelligence to come in and develop things, and work out where PFT goes now.

“The thing about PFT is that it's always about evolution, not revolution. The changes that have occurred in my time in Pitlochry have been slow and gradual, but whoever takes over my job will be starting from a very different position to when I first came in.”

In terms of specific examples where the artistic envelope has been pushed, as well as the Scottish contemporary work, Durnin singles out productions of Frank McGuinness' play, Dolly West's Kitchen, Ronald Harwood's 1995 drama, Taking Sides, and Alan Ayckbourn's Snake in the Grass. Another stand-out was the Scottish premiere of David Greig's play, Pyrenees.

“For a show like that to do so well shows how far we've come as a company,” says Durnin, who remains coy about what he might do next.

“This job has been a constant,” he says. “PFT programmes are more work in a year than any other theatre in Scotland, so in the first instance I think I need to give myself the space to think about what it is I want to do next, and where my future lies.

“It will be a huge wrench leaving Pitlochry. I'll miss everyone who works here hugely. Pitlochry operates in a very specific way, and it's a real team effort putting on those shows. These are people who understand why we want to work here. While I'm talking to you now, I'm looking out of my office window at this beautiful Perthshire landscape, and I can see a ben with snow on top. Whatever I do next, I'm never going to get that again.”

Beyond Singin' in the Rain, Durnin's last gift to Pitlochry is his programming of the theatre's 2018 summer season. This will kick off with Chicago, another musical more often seen in receiving houses. There will be more music in Jim Cartwright's play, The Rise and Fall of Little Voice, while following the success this year of Mary Rose, the 2018 season will feature another JM Barrie play, Quality Street. Also in the programme will be a production of Tom Stoppard's 1974 comedy, Travesties, a version of Somerset Maugham's short story, Before the Party, and a production of Rona Munro's play, The Last Witch, its first since premiering at Edinburgh International Festival several years ago.

Plans are also in place for an ambitious capital project to develop PFT's building, making it fit for the 21st century. Durnin won't be around to see this, and, despite him choosing next season's plays, neither will he be returning as a guest director.

“One mustn't haunt the place,” he says. “If you're saying goodbye, then you have to go.”

While Durnin's legacy at Pitlochry will linger a good while yet, for all its sense of renewal, Pitlochry Festival Theatre will retain its unique identity.

“I hope the ambition for the range of the repertoire will continue,” says Durnin, “and I'm hoping it will hang on to its ensemble practice and its repertoire system. If you're starting out as a performer, a director or a designer, working alongside more experienced people across six or seven shows, you learn an extraordinary amount, and you learn about working with people in a very different way than if you were just doing one show over seven weeks. That's the heartbeat of Pitlochry Festival Theatre, and long may that continue.”

Singin' in the Rain runs at Pitlochry Festival Theatre until December 23. Tickets for PFT's summer 2018 season are on sale now.

www.pitlochryfestivaltheatre.com