OF all the gin joints in all the towns in all the world, the Victorian Bar in Glasgow's Tron Theatre is more atmospheric than most.

It should, then, lend itself perfectly to its forthcoming transformation into Rick’s Bar for post-show drinks following performances of Morag Fullarton’s stage adaptation of Casablanca in the main house. Even before the bar’s forthcoming makeover, sitting alone at a table on a wet Wednesday afternoon waiting for a woman you’ve never met before and without so much as a piano player to set an extra layer of melancholy, one can’t help but feel like you’re already part of the movie.

When Fullarton arrives from rehearsals, we’re returned in an instant to the Glasgow where this most singular of writer/directors cut her theatrical teeth before moving into television, working on dramas such as This Life, Taggart and Rebus. At the moment, it’s her three-actor version of one of the most iconic films that concerns her.

“I love it!” Fullarton gushes from the off about the movie that paired Humphrey Bogart and Ingrid Bergman in wartime Morocco for one of the greatest unfulfilled on-screen romances in celluloid history. “It’s got tremendous heart, and there’s a fascinating combination of a huge moral dilemma and a great love story.”

Casablanca also has some of the most familiar lines ever misquoted, from Bergman’s: “Play it, Sam” line that leads to the club pianist playing As Time Goes By, to Bogart’s final: “This could be the start of a beautiful friendship”.

“I knew the first time I saw it I’d seen something special,” says Fullarton. “Films like that aren’t made today. There’s nothing quite like Casablanca.”

The idea for putting Fullarton’s favourite film on stage came from Classic Cuts, Oran Mor’s A Play, A Pie And A Pint offshoot of slimmed-down Shakespeares and other works from the canon. Fullarton suggested to producer David MacLennan that a treatment of a classic film was equally valid, and duly set to work.

The result, when it first appeared as what Fullarton styles as the “lunchtime cut” of the show was a rip-roaring success, duly being lauded with a five-star review on these pages. More homage than pastiche, Fullarton’s new “gin joint cut” of her play now comes with her script pretty much untouched, but with a real-life B-movie shown before the main feature.

“We’re not trying to stage the movie,” she’s quick to point out. “We’re doing a piece of theatre, so the way I approached it was to try and make a great theatrical event. Part of what happened was that I took what I thought were the best bits of the film and cut out quite a lot.

“You have to be careful you don’t fillet it too much or throw the baby out with the bathwater, but part of the fun of the staging for the audience is seeing the actors play all the parts, and it seems to work. You have to be careful when you’re dealing with something that’s so cinematic, because you’re working in a different medium.”

For a piece of work that necessitates the appearance of the army of the Third Reich, this is just as well. Fullarton’s first-hand experience of one medium being transferred to another without adapting to its new form is in fact responsible for her own leap from stage to screen.

“My first experience of putting something on screen was a televised version of my stage production of Mistero Buffo for BBC Two,” she recalls. Her production of Dario Fo’s play starred Robbie Coltrane, “and I was so deeply disappointed with how they televised it, I decided to learn how to do it myself. You can’t just point a camera at a stage and hope for the best. So by the same token I’m very aware that I’m not putting a film on stage. I’m turning this into a theatre show, with all the craft and the magic that will work for an audience. That’s what we have fun with, the things you can do on stage that you can’t do on film.”

While the publicity material for Casablanca describes it as “disrespectful”, Fullarton is at pains to point out that her take on it is not a spoof or a pastiche.

“It’s affectionate,” she says, “but it’s respectful in that I’ve gone for the best lines. I think sometimes there’s a snobbery with people who say that movie scripts can’t compare with theatre scripts, which is something I don’t agree with. I think there’s some great writing in film, and I think there’s some terrific moments in the writing to be enjoyed in Casablanca. So from that point of view, yes, it’s respectful to the script. The disrespectful thing comes in other ways, and I think you’d have to have a very thin skin to get upset by some of the devices we’ve used to make it work with three actors playing all the parts. So it’s more we’re taking license with it than being disrespectful per se.”

This isn’t the first time Casablanca will have been seen on stage. Long before Fullarton’s versions, the 1942 film was based on Everybody Comes To Rick’s, by Murray Burnett and Joan Alison, who sold their script to Warner Brothers in 1942 for $20,000 after failing to find a Broadway producer.

While much of the play remained intact in the script for Casablanca, including the use of the song As Time Goes By, Everybody Comes To Rick’s has only seen one high-profile production. That was in 1991, when former EastEnders bad boy Leslie Grantham played Rick. “Apparently the original play was dreadful,” says Fullerton, only knowing the play by reputation.

While a slow-burner on its initial release, the film has since acquired a status that might well cause acolytes to be protective.

“People were coming up to me and saying, ‘That’s my favourite film, I hope you’re not going to mess it up’,” Fullarton says. “But then they’d come and see it, and I don’t think anyone thought we’d done something terrible to the film. I can say that because we’ve done it, and one of the reasons we’re doing it again is because people were fighting to get in to see it.

“But I also think we’re reinventing it for a different kind of audience. Another of the reasons I wanted to do this was because it’s one of my favourite films, but the only time I ever have to see it on a big screen is occasionally once every five years or so at the GFT or something. Now, wouldn’t it be great to have the opportunity for all the people who feel the same as me to see this irresistible cocktail of a film done in a different way?”

Here’s looking at you, kid.

Casablanca: The Gin Joint Cut, Tron Theatre, Glasgow, July 7-23; Pleasance, Edinburgh, August 3-29. Visit www.tron.co.uk and www.pleasance.co.uk.