The longest runner in Broadway history and London’s second-longest after world record holder “Les Miserables,” “The Phantom of the Opera” has amassed global grosses of more than $2.63 billion. With box office revenues higher than for any film or stage play in history, including “Titanic,” “E.T.” and “Star Wars,” it has been seen in 144 cities in 27 countries by more than 100 million people.

Thus the most daunting problem for Andrew Lloyd Webber’s follow-up, “Love Never Dies,” is great expectations.

The official line from Lloyd Webber’s Really Useful Group is that the latest musical is not a sequel but a “continuation” of “The Phantom of the Opera.”

And small wonder — outside of three “Nunsense” follow-ups, musical theater has never pulled off a hit sequel. The shortlived “The Best Little Whorehouse Goes Public” and the even shorter “Bring Back Birdie” (four perfs) stand as evidence.

On the plus side, Lloyd Webber’s £6 million ($9.25 million) new tuner arrives with a readymade marketing hook via all those potential ticketbuyers who have already bought into the story — having experienced “the brilliant original,” the phrase currently emblazoning London posters for “Phantom.”

Helmer Jack O’Brien (“Hairspray,” “The Coast of Utopia”) has been on board for about 2 1/2 years. He’s clear-eyed about the pros and cons of this unique property.

“No one will thank us for doing this,” he tells Variety. “I have said that since the beginning. This is not something you do as a lark, without a sense of responsibility. Whatever one thinks of the first show, it has gone into the imaginative repertoire of its audience.”

O’Brien points out that according to Lloyd Webber, when “Phantom” opened in 1986, the smart money was on rival tuner “Chess.” The latter premiered five months earlier but only managed a run just shy of three years. “‘Phantom’ just slipped in,” says O’Brien. “Then whatever happened, happened.”

He believes the original’s global success means the new show will be scrutinized “probably unfairly,” but O’Brien remains buoyant. The book — on which he worked alongside a slew of collaborators past and present including Frederick Forsyth, Ben Elton and lyricist Glenn Slater — is set 10 years after “Phantom” amid the eerie fairgrounds of Coney Island. The aim is not unlike the sequel-meets-prequel approach of “The Godfather Part II,” which improved upon the original.

These days, Lloyd Webber is arguably more famous as a showbiz mogul than as a composer (his most recent new tuner, “The Woman in White,” was not a financial success). Not only did he produce Jeremy Sams’ hit revival of “The Sound of Music,” he made himself immensely visible — and successful — as “The Lord” on primetime BBC TV, judging talent shows that cast leads in his productions. (Lloyd Webber will revisit that role later this year, casting his forthcoming revamp of “The Wizard of Oz,” skedded for 2011.)

For “Love Never Dies,” he has eschewed TV casting, instead hiring Ramin Karimloo as the Phantom (he has played the role in the original onstage) with Sierra Boggess (“The Little Mermaid”) as Christine.

Lack of TV pre-sell, however, hasn’t harmed bookings. Where “The Woman in White,” opened in London in 2004 to a $4.6 million advance, “Love Never Dies” currently stands at $12.3 million. That said, the figure wilts in comparison with Cameron Mackintosh’s 2009 “Oliver!” revival, which opened to a record-breaking $23 million.

Really Useful Group chief executive Andre Ptaszynski tells Variety the show needs to take $50.9 million to fully recoup. In the 1,500-seat Adelphi Theater, that will take a year. But RUG owns the much larger London Palladium and Theater Royal Drury Lane. Why not choose either of those?

“Essentially, it’s a love story and so it needs a more intimate space that will make it more fulfilling for the audience,” Ptaszynski says. “And if it works, it’s likely to sit longer and more happily in a smaller theater.”

One of the key factors determining the hoped-for longevity of “Love Never Dies” is the surrounding economic and cultural climate.

The design and sheer spectacle of both “Les Miz” and “Phantom” helped define their era within a booming economy. Attendances in both London and Gotham have unexpectedly risen during the recession, but the chances of a new, non-jukebox show sticking around are slim. With the exception of the phenomenon that is “Wicked,” the survivors these days are either back-catalog tuners like “Mamma Mia!” or Disney’s revamps of its movies, “Beauty and the Beast” and “The Lion King.” Even those have lately shown less traction — witness “The Little Mermaid” and “Tarzan.”

As with most grand-scale tuners, “Love Never Dies” has had pre-opening problems, beginning with the aborted idea of near-simultaneous openings in London, New York and Shanghai, dreamed up 15 months ago by Ptaszynski and Lloyd Webber.

“After a couple of months, we realized the folly of our ways,” Ptaszynski says.

The new rollout for the show allows more room to maneuver.

“We expect to announce a late fall opening on Broadway,” Ptaszynski says. “There’s lots of working time in the spring if needed.”

The show’s March 9 London preem was postponed from six months earlier to allow for a comprehensive redesign and reorchestration. Then, a surprisingly brief technical rehearsal period in the theater forced the cancellation of the first preview. At the subsequent first performance, a technical hitch caused everything to grind to a temporary halt.

That, however, is par for the course for new tuners. During the original “Cats” rehearsals Judi Dench was forced to withdraw from the role of Grizabella when she snapped her Achilles tendon — which is how Elaine Paige got to sing “Memory.”

One thing is certain. The show has a buzz. When details of the forthcoming CD appeared online, hundreds of the original’s self-styled “Phans” began blogging feverishly, trying to work out the plot from song titles.

Whatever the pressure, as O’Brien tells it, he’s not frightened.

“I’m exhilarated. Getting over, around and past the success of the original will be a kind of victory,” he says.

What sort of victory remains to be seen.