You mean they still turn musicals into films? You can be forgiven for asking the question, since so much of the traffic has been hurtling in the other direction of late, theatrical impresarios filling the stage with big budget adaptations of screen hits. Although the wreckage of Gone with the Wind has just been carted away from the West End, the transatlantic success of The Producers, Billy Elliot and the like has raised fears that the theatre is turning into a subsidiary of the film industry. Once a cornerstone of the Hollywood edifice, musicals have become an optional accessory. It was striking that when Sweeney Todd finally reached the cinema, the trailer left many a filmgoer convinced that the music itself had suffered the same fate as Mr Todd's poor clients.

So some traditionalists will have been cheered by the news that a remake of My Fair Lady is in prospect, with Keira Knightley reportedly filling Audrey Hepburn's dainty shoes. And now we have the screen version of Mamma Mia!, a show that proved an unlikely launch pad for an Abba revival. West Side Story it ain't, but given the dearth of inventive new commercial musicals, audiences are inclined to be grateful for every crumb that comes their way. (Is anyone up for sitting through Lasse Hallström's early opus, Abba: The Movie? No, I thought not, although I'd happily watch a re-run of Muriel's Wedding, a comedy that makes ingenious use of those synthetic Scandinavian evergreens.)

Mamma Mia! has been re-packaged by the trio - director Phyllida Lloyd, producer Judy Craymer and writer Catherine Johnson - responsible for the West End hit that opened for business in 1999 and went on to conquer America. The breezy, upbeat story of a young bride-to-be who seeks out her real father on the eve of her wedding on a Greek island has been fitted out with an A-list cast including Pierce Brosnan, Meryl Streep and Colin Firth. Since some 30 million people have seen the stage version, the film-makers ought to have a fair idea of their target audience.

In truth, these are - relatively speaking - propitious times for screen musicals. After lingering in a near-death state for some two decades, the genre has enjoyed a modest resurgence. Baz Luhrmann's Moulin Rouge! (2001) is given the credit for applying mouth-to-mouth resuscitation, and all the Oscars that showered down on Rob Marshall's adaptation of Chicago (2002) suggested that one of Hollywood's most durable formats had begun to find its feet again.

Whether we will ever enjoy another golden age remains to be seen, of course. One reason why the period that roughly spanned the 1930s to the early 1960s was so fertile was that musical theatre was harnessed to an extraordinarily inventive popular music culture, in which sophistication and wordplay were prized qualities. While contemporary pop has its virtues, few would argue that it has made the ideal match for Broadway (Grease being the prime exception to the rule). Perhaps we will have to wait another generation to see what a new crop of theatre writers, imbued with post-MTV values, will bring to the table.

At the most practical level, film musicals are good for the theatre simply because they are often the easiest way for listeners to enjoy high-quality productions. Your average multiplex may be a sterile place, but it can still provide the ideal introduction to the art of song and dance.

Some films have come close to displacing the original productions in the public's imagination. When people think of West Side Story, for instance, it is invariably in terms of the movie's colour-drenched, wide-screen vistas. Stephen Sondheim's biographer, Meryle Secrest, goes as far as to claim: “If West Side Story had never become a film, its score would have languished in obscurity.” Just as the wide-open plains become part of the supporting cast in the handsome film of Oklahoma!, so Robert Wise and Jerome Robbins brought the sidewalk to life.

Ironically, Sondheim - who provided the show's lyrics - doesn't seem to share the public's high regard for the movie. As he explained in one recent interview: “In West Side Story you see a gang dancing down a real New York street in colour-co-ordinated sneakers, and you just don't believe it. And then there are the songs themselves. The problem is, what do you shoot in something like Tonight? You get a close-up of him, a close-up of her, a medium shot of the fire escape ...

“The director has to fill out three or four minutes of what is essentially a static song, which holds your attention on the stage because that's part of the theatrical convention. Whereas for me, as a movie buff, I want the action to move forward constantly, and it doesn't. They may have little camera diversions and a trick here or there, but they're just filming a stage musical, and that's not for me.”

Is there a formula for creating a hit adaptation? Obviously not. Film is the ultimate realist medium, and each director has to find a way of drawing the audience into what is, on the face of it, the highly unreal convention of characters bursting into song. And while shows usually feed off the energy of a live audience, a movie adaptation has to find its own sustenance. Which goes some way to explaining why Susan Stroman's doggedly unadventurous screen version of The Producers - which might have seemed to have the makings of a sure-fire hit - simply curled up and died.

In the golden age of Technicolor, sheer spectacle carried many a mediocre show. (In the case of South Pacific, the unbearably lush cinematography actually proved a liability.) For all their virtues, some vintage musicals do look static now. With the advent of Bob Fosse's Oscar-winning version of Cabaret, a hint of dark irony became an ultra-hip accessory. (You can't help wondering what The Sound of Music - a delightful film on its own terms - would have looked like if Fosse had got his hands on it.)

The screen adaptation of Chicago, another sardonic work from the pen of Kander and Ebb, boasts a similarly dark landscape. Too relentlessly dark, some would say. But the punters - and the Oscar voters - disagreed. Mamma Mia!, for good or ill, is awash with sunshine.

Mamma Mia! is released nationwide on Thursday

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