Is it time West Side Story got a 21st-century makeover?

This month, 'West Side Story' returns to the London stage in a form unchanged since 1957. Time for a 21st-century makeover? Certainly not, says its original lyricist, Stephen Sondheim...

Two woodwind players sneak in fast with an insistent cross rhythm, expectation shimmers on the air... "Could it be? Yes it could/ Something's coming, some-thing good/If I can wait!/ Something's coming, I don't know what it is/But it is/Gonna be great!"

That's not just Tony's opening number from West Side Story, it's as good a description as you'll find of the entire genre-busting show, the now legendary musical transplant of Romeo and Juliet to gangland Manhattan. And although its latest production doesn't open in London until 22 July, there's one incontrovertible reason why the musical-theatre industry expects it to match that expectation: it's not really new at all. This is less of a production, more a reproduction.

Trevor Nunn and John Caird's Les Misérables may be the same across 38 countries and in 21 languages, but that's because it's still the original production, which has never closed. Revivals are a different matter. Whether you're directing The Taming of the Shrew or Kiss Me Kate, the job is all about presenting the work afresh. But not with West Side Story.

You don't have to imagine what Broadway critics saw – and largely raved about – on its original 26 September 1957 opening night, because an exact facsimile of that is all the lawyers will allow. Not for nothing is this billed as "The 50th Anniversary Production". This is a masterpiece and no one's messing with it.

Back then, its creative quartet boasted two headline names: director/choreographer Jerome Robbins and composer Leonard Bernstein. The "book" (adaptation, structure and dialogue) was by screenwriter and playwright Arthur Laurents and the lyrics were by a 25-year-old making his Broadway debut.

That 25-year-old, Stephen Sondheim, is now regarded as musical-theatre's greatest iconoclast, who regularly gives the nod to intelligent rethinks of musicals he has written on the grounds that while a director must do what Sondheim wrote, how he or she chooses to do it is up to them. He recently applauded a version of Sunday in the Park with George in London that completely reimagined the show via video projection, and went on to win five Olivier awards. So it's something of a surprise to discover that he is unperturbed by the stringent demands of the Robbins estate. Isn't their policing of the piece in danger of creating museum theatre?

"In that context, 'museum' is a pejorative term," he counters. "Yes, West Side Story is a preserved object that's locked into place. But you could just as easily call it a classic."

This show, he argues, is not like other musicals that stand or fall by their score and book. It's closer to a ballet where every step, moment and movement is precisely notated so that it can be endlessly recreated.

"Choreographed movement is central to its storytelling and structure. Although much of the dance music was technically written by Jerry's assistant Betty Walberg, Jerry's choreography is still so apt because he worked so closely with Lenny [Bernstein], just as they had done on their ballet Fancy Free. Whether another choreographer could match that level of inspiration, I don't know."

Sondheim isn't using 20/20 hindsight to be overly generous. Robbins was, to a great extent, the show's prime mover. It began life in a discussion at his home where he persuaded Bernstein and Laurents to create a contemporary Romeo and Juliet set on the Lower East Side during Easter/Passover with a Catholic Romeo and a Jewish Juliet. Laurents began a scenario for East Side Story but with everybody's diverse commitments, the project foundered. Six years later, poolside at the Beverly Hills Hotel, when Bernstein was in town to conduct at the Hollywood Bowl, he and Laurents clocked newspaper headlines about teenage Latino gangs and the idea swung into focus.

Anyone watching the musical they made, or the 10-Oscar-winning film, cannot fail to spot that it's driven by dance. At considerable cost to his producers, Robbins demanded double the rehearsal time – eight weeks instead of four – so that he could also choreograph it. And he made damn sure everyone knew it: ever since the initial tryout in Washington, all publicity for the show has to bear the legend, "Based on a Conception of JEROME ROBBINS." The writers' names follow, also in capitals, but beneath them in a separate box comes the killer: "Entire Original Production Directed and Choreographed by JEROME ROBBINS."

That's less surprising when you know that by this time Robbins not only had a string of Broadway hits to his name, but was also one of America's leading ballet choreographers. Though he died a decade ago, the controllers of his estate stick zealously to his will, and reinterpreting his choreography for contemporary audiences remains forbidden.

Until recently, that stipulation stretched to design. Stage design dates as fast as any other kind and, 10 years ago, when the show last toured the UK, Oliver Smith's original sets seemed not so much revived as exhumed. Painted backdrops may have looked beautiful in 1957 but theatregoers are now used to a different aesthetic. And so the estate has relented: the current revival has new sets – lots of scaffolding – costumes and lighting.

Part of Sondheim's antipathy to tampering with the original may stem from his reaction to the film. Robbins wound up with an Oscar for his efforts but he had been sacked less than halfway through the shoot so much of his vision never reached the screen.

Sondheim is clear-eyed about it. "Theatre is about the audience's imagination, movies are not. They could not find a way of translating stage language to film language. I found it all too pretty, with self-conscious scenes of candy-colour-co-ordinated washing and sneakers. Having the gang dance down the street isn't frightening, it's fun. One of my favourite stage images is what Jerry called 'the leapfrog'. Seeing three actual bodies, 450 pounds of beef, leap over people on stage feels menacing. On the screen it just looks like leapfrog."

Sondheim is currently reworking the show for yet another "revival" for Broadway's 2008/09 season directed by Laurents, who is soon to turn 90. With the exception of Maria, firebrand Anita and possibly her brother Bernardo, the Puerto Rican gang of Sharks will now speak only Spanish. "I'm not sure yet how we will work out the lyrics, and how or why they will sing in English, but we're already casting." Robbins's physicality, however, will remain untouched.

The rights holders are evidently of the "if it ain't broke, don't fix it" school. But if they're not careful, West Side Story will ossify. Isn't it time the keepers of the Robbins flame had the courage to let dynamo director/choreographers such as Rob Ashford, Matthew Bourne or Susan Stroman take this masterpiece out of the museum and into the 21st century?

Can't touch this: Four more protected stage masters

Samuel Beckett, 1906-1989

Beckett's literary executors keep his plays in a vice-like grip. The director Deborah Warner was banned from directing his works for more than a decade after her 1994 production of his play Footfalls contravened two stage directions

George Balanchine, 1904-1983

Any company wishing to dance the Russian-American choreographer's work has to win his Trust's approval, which it can, and does, withdraw if it's unhappy. In the past, even the Royal Ballet has not been spared the Trust's wrath

Kurt Weill 1900-1950

If you want to stage a show by Weill, you have to comply with his Foundation, whose executors have been known to haggle over whether a song in one of his musicals should be allowed to be transposed by as little as a semitone

Elvis Presley 1935-1977

Elvis Presley Enterprises banned Peter Schaufuss's "dansical" The King – a hit in Denmark – for using material and Elvis's persona without permission. Schaufuss chose other songs, turned the character into an impersonator and the show went ahead in London. It bombed

'West Side Story' is at Sadler's Wells, London EC1, from 22 July until 31 August. ( www.sadlerswells.com), then touring ( www.westsidestorytheshow.co.uk)