The West End revival of Andrew Lloyd Webber’s “Whistle Down the Wind” has one big advantage: It got in early. The show’s March 27 opening put it ahead of an astonishing pack of 13 more tuners opening in London this year.

As Adam Kenwright, managing director of theater advertising and marketing agency AKA, puts it, “All this new product represents the most exciting period the commercial theater has had in the last 30 years, if not ever.”

He’s not exaggerating. Heavyweight U.S. titles “Wicked” and “Monty Python’s Spamalot” seem likely to dominate the fall season, the former having already beaten its U.K. producers’ expectation by taking an initial £2 million ($3.5 million) six months ahead of opening.

Official London box office figures are as closely guarded as state secrets, but insider indications are that “Spamalot” and fellow fall arrival “Dirty Dancing” are taking similar amounts, a notion bolstered by the latter’s record-breaking business in Germany.

Anthony Pye-Jeary, managing director of Dewynters, the agency handling at least six of the newcomers, is skeptical of the obsession with advances. “Producers always want to play their advances off one another, but anyone who says they know how to get an audience into a show that hasn’t opened yet is exaggerating their expertise.”

He’s as happy as anyone to be racking up money ahead of the game, but he doesn’t believe it’s the crucial figure.

“What really matters is what you do the day after you open,” he says. “On ‘Chicago,’ (producer) Barry Weissler was worrying that at £20,000 a day we weren’t taking enough. I said, ‘Hold your horses.’ After it opened we took nearer £200,000 a day.”

Dewynters is handling both of the shows with Lloyd Webber’s name attached as producer, starting this fall with Webber’s long-cherished revival of Rodgers & Hammerstein’s “The Sound of Music” at the 2,255-seat London Palladium (dates still to be announced). Helmed by Jeremy Sams, it will be bolstering ticket sales with a search-for-a-star TV series set up to find its leading lady. Before that, Michael Grandage will direct the highly anticipated first major revival of “Evita.”

Dewynters also will be responsible for “Avenue Q,” co-produced by Cameron Mackintosh. When not overseeing the London version of the anarchic puppet musical, he’s acting as landlord to the U.K. touring production of “Footloose” — already in previews at his Ivor Novello Theater — and Sam Buntrock’s startling new take on Sondheim and Lapine’s “Sunday in the Park With George,” which transfers May 13 from the small, entrepreneurial Menier Chocolate Factory to the 750-seat Wyndhams in the West End.

Three other upcoming tuners have one thing in common — predominantly black casts — but are indicative of the immense diversity of product on show.

“Daddy Cool,” the four-month-delayed jukebox musical of Boney M and Milli Vanilli hits, will open at the Shaftesbury; the National Theater will host the U.S. production of Tony Kushner and Jeanine Tesori’s “Caroline, or Change”; and Trevor Nunn is due to close out the year with a new version of “Porgy and Bess.”

A theater has yet to be announced — the hot money is on the Savoy — but Howard Panter of the Ambassador Theater Group will co-produce this slimmed-down version of the Gershwin classic, with new orchestration for wider musical theater exploitation by Gareth Valentine.

Kenwright sees all this as a boom time. “London is very, very rich. For the second year running we have beaten Paris to be the most populated and successful tourist destination in Europe, with a 37% increase in European visitors year-on-year for the last two years.”

Meanwhile, the West End hit record attendance of almost 13 million last year. “We know it will be nearer 13.5 or 13.75 (million) this year,” Kenwright says. “If ‘The Lord of the Rings’ with its specific audience comes in to the Dominion in 2007, that could bring the figure up to 14.25 million. That’s an amazing 13% or 14% rise in two years.”

That notion of specific audiences is echoed throughout the industry. As Caro Newling of Neal Street Prods., one of the producers of “Sunday in the Park” puts it, “All these musicals are very bespoke.” “Spamalot,” she argues, can absolutely co-exist beside “Wicked” because they cater to different tastes.

Newling believes good theater produces not only good word of mouth but the likelihood of cross-fertilization. “Playing opposite ‘Avenue Q’ and around the corner from ‘Mack and Mabel’ must be good for all of us.”

The real question is less about which of this bumper crop — which also includes a limited 16-week run for the Twyla Tharp-Billy Joel project “Movin’ Out” — will survive, but how they will affect the rest of the economy. Clearly, the days are numbered for any of the current long-runners already struggling. Once again, no one is willing to name names, but revivals that need revamps via cast changes are more susceptible in a market dedicated to the shock of the new.

For the advertising agencies, there’s a lot to play for. Pye-Jeary believes a producer looking for global rollout of a show needs to be holding around $1.75 million in readiness to fully fund a campaign.

He’s also confident that the wider latitude of U.K. advertising — traditionally more adventurous and less literal-minded than its U.S. counterpart — offers opportunities for agencies and producers to have fun while taking audiences seriously.

“Just as on ‘The Producers,’ where our opening ads were far more risque than the U.S. production, on ‘Spamalot’ we feel British audiences can take a little more of Monty Python rudery,” says Pye-Jeary. “For example, Spam is to create a new brand, ‘with stinking French garlic.’ ”

Meantime, back at the bigger picture, Kenwright sounds a note of warning. “Are the musicals going to suck the playgoers a bit? Will the plays struggle? Maybe. That’s where the industry really will have to work hard.”