The seventh and penultimate Harry Potter movie has its world premiere in London on Thursday, with another big pay day virtually guaranteed for studio Warner Bros. despite its failure to get a 3-D version ready in time.

Young British stars Daniel Radcliffe, Emma Watson and Rupert Grint, who play Harry, Hermione and Ron respectively in the wizard series, are expected on the red carpet for "Harry Potter and the Deathly Hallows: Part 1" due in theatres on November 19.

Warner decided to split the seventh and final J.K. Rowling book about Harry and his wand-wielding adventures into two films after the first six movies amassed a staggering $5.4 billion at the global box office.

Yet the hugely popular franchise has yet to break the billion-dollar barrier with a single title, and a 3-D release would have made that landmark a near certainty, experts said.

"I think the 3-D issue must be a big disappointment for Warner Bros." said Andreas Wiseman of Screen International.

"I think they've really missed a trick. Other big franchises like 'Saw', 'Shrek' and 'Toy Story' have gone from strength to strength (by turning to 3-D)."

He added that Deathly Hallows Part 1 may cross $1 billion in global ticket sales even without higher prices commanded by a third dimension, and that the franchise has another chance to cash in on 3-D with Deathly Hallows Part 2 out next July.

HUNT FOR HORCRUXES

In Deathly Hallows Part 1, Harry, Ron and Hermione set out on a mission to track down and destroy the secret to evil Lord Voldemort's immortality and destruction -- the Horcruxes.

The movie trailer, part of a major marketing campaign running for several weeks already, suggests the film will feature a familiar mix of spectacular action sequences and increasingly dark storyline with the added twist of a bust-up between close friends Harry and Ron.

The actors playing the three central characters for the last decade are in the middle of a grueling round of interviews to promote the film, and have spoken of mixed feelings about a franchise that turned them into A-list stars and millionaires.

Grint, 22, felt a sense of relief that a decade of filming had finally ended.

"It's just really great, it's a sense of real freedom because filming on Harry Potter...it does take over your life and it is really long shoots and it's just nice to be out and do your own thing for a change," he told Reuters.

Watson, 20, who was Hollywood's highest paid female star in 2009 according to Vanity Fair, explained how she turned to fashion to help her distance herself from Hermione.

"Fashion was my way of being myself away from the part of Hermione," she said.

"It was my way of expressing who I was and that we were two different people. So it's something I really got into and something that I really love and I just felt it allowed me to be myself."

Radcliffe, 21, cast as Harry in 2000, said he was unlikely to reprise the role even if Rowling were to pen another novel.

"I think 10 years is a long time to spend with one character," he told Sky News.

He has also described the Potter films as "rather like the mafia. Once you're in, you're never out."