London ? Mary Poppins is back — and producers hope she retains her magical powers.

The no-nonsense nanny who whisks a pair of London children off on supernatural adventures has delighted generations of youngsters. Seventy years after she arrived in a book by P.L. Travers — and 40 years after Julie Andrews floated on-screen under an oversized umbrella in the film adaptation — there are signs that Mary Poppins can still cast a powerful spell.

A big-budget stage musical opens Wednesday. It is one of the year’s most anticipated West End shows.

Thomas Schumacher, head of co-producer Walt Disney Co.’s theatrical division, is certain that Mary Poppins’ enduring qualities — “magic, zaniness, inappropriateness, a curious disrespect for authority” — will thrive onstage.

“One thing Mary Poppins says, in the book and in our show, is, ‘I never explain anything,”‘ Schumacher said. “That allows her extraordinary freedom. We don’t even know who the heck this woman is. Is she a witch? Is she a fairy? Is she a guardian angel? She explodes into the imagination.”

London’s theater community hopes Travers’ enduring creation will be the spoonful of sugar the struggling West End needs. Apart from the Mel Brooks musical, “The Producers,” which opened last month to rave reviews and a healthy box office, London’s theaterland has been bedeviled by a string of underperforming shows.

“Mary Poppins” certainly has a sterling pedigree.

Rare collaboration

The musical is a rare collaboration between West End mega-producer Cameron Mackintosh (“Les Miserables,” “Mamma Mia!”) — who owns the stage rights to Travers’ Poppins books — and Disney, which owns the songs and story lines from the 1964 movie. After years of impasse, the two sides agreed in 2001 to collaborate on a stage adaptation.

“It looks on paper like it would be a complicated relationship,” conceded Schumacher, an affable Californian who relocated to London last year to help shepherd the show to completion. “But when it comes down to me and Cameron, we had so many of the same tastes, the same instincts, the same kind of people we want to work with.”

A SCENE FROM A DRESS REHEARSAL OF THE MUSICAL MARY POPPINS in the Prince Edward Theatre in London. The show premieres Wednesday with Laura Michelle Kelly, right, playing Mary Poppins.

That list of collaborators includes director Richard Eyre, former head of Britain’s National Theatre, and choreographer Matthew Bourne, creator of a renowned all-male “Swan Lake” and the Olivier award-winning “Play Without Words.” Laura Michelle Kelly, a much-praised Eliza Doolittle in a West End production of “My Fair Lady,” stars as the enchanted nanny.

The show’s book is by Academy Award-winning scriptwriter Julian Fellowes (“Gosford Park,” “Vanity Fair”), while composer George Stiles and lyricist Anthony Drewe have written six new songs to complement the film’s tunes by brothers Robert and Richard Sherman.

“There are big personalities involved, so, of course, there’s the odd screaming match,” said Stiles, working in his west London studio a few days before opening night. “Of course, there’s the odd severe creative disagreement about how one should solve something. But it’s not mad egos bumping up against one another. It’s entirely fair to say it has been a happy experience.”

Closing generation gap

Fellowes said in an article he wrote for the Sunday Telegraph that his biggest challenge in adapting the work “lay in the Poppins generation gap” — appealing both to fans of the 1930s books and of the 1960s film; to those who cherish Julie Andrews’ sympathetic Mary and those who love the plainer, vainer character described by Travers.

The same is true of the songs. Stiles and Drew, whose work includes the Olivier award-winning musical “Honk,” have had to create new songs to fit in amid tunes — “A Spoonful of Sugar,” “Supercalifragilisticexpialidocious” — that are known and loved by millions.

LAURA MICHELLE KELLY plays Mary Poppins. Kelly performed as Eliza Doolittle in a West End production of My

“It’s such a double-edged sword, because if we’ve done our job well, people are not going to know we’ve written anything new,” said Drewe with a laugh. “And if they do think we’ve written anything new they’re going to hate us.”

“A stage musical based on Mary Poppins without the Sherman brothers’ songs is unthinkable,” said Stiles. “As Richard Eyre describes it, they’re like our musical DNA. We’ve absorbed them by osmosis into our collective psyche. One of the nicest things Dick Sherman has is said there are places where he simply can’t tell where he’s left off and we’ve begun.”

But does the world of “Mary Poppins” still speak to audiences? While the Edwardian affluence of the Banks family’s life on Cherry Tree Lane is cozily nostalgic, the show’s creators say its emotional tone is strikingly modern. Eyre has said that the story “is about an unhappy family being healed.”