IT is enough to make every boy and girl muggle scream with delight - the third instalment in the Harry Potter series will be in cinemas across Britain four days earlier than expected.

Due to ''exceptional demand'' from Pottermaniacs, the public will be able to see Harry Potter and the Prisoner of Azkaban on the last day of May, which is also a bank holiday Monday.

Warner Bros confirmed the UK general release has been brought forward to May 31, guaranteeing that children off school will be packing out cinemas that day.

The film, the first in the series to be released in summer, faces fierce rivalry from Shrek 2 and Spiderman 2.

The stars are expected to come out for the world premiere of the film tomorrow at the Radio City Music Hall in New York , and for its premiere in Leicester Square, London, the day before its release.

Robbie Coltrane, who plays Hagrid, Michael Gambon, who has succeeded the late Richard Harris as Dumbledore, and Daniel Radcliffe, who plays Harry, are due to attend. JK Rowling, the Edinburgh-based author of the books about the schoolboy magician, will not be at the New York premiere, but will attend the London event.

Trailers and private screenings show that Harry Potter and the Prisoner of Azkaban is darker, deeper, and scarier than previous episodes in the series.

Fans are in for a fright when they see the film's numerous ghoulish scenes, including the first appearance of the hooded, wraith-like dementors - the jailers of Azkaban prison - and a snarling werewolf.

The change in tone of the film has been attributed to Alfonso Cuaron, its Mexican director, who has taken over from Christopher Columbus.

The film lasts 136 minutes, the shortest of the series so far.

It focuses on the fate of an accused murderer and Harry's godfather, Sirius Black, played by Gary Oldman, who escapes from Azkaban Fortress and comes after Harry.

Harry also gains new insights into his peculiar past, including Black's close association with his family.

Steven Gaydos, of Hollywood magazine Variety, said that he is in no doubt the film will be successful.

He said: ''The bar has been raised so high for sequels these days, with Lord of the Rings and the previous Potters all getting near the $1bn mark, but I would say that it will still be a success for Warner

Brothers.''

Cuaron has said that he and Columbus have approached the saga in different ways.

Cuaron - who had never read a Harry Potter book or seen a Harry Potter film before he took the job - wanted to focus on the book's characters.

''Hopefully there will be more readings to the film, the same as you can have more readings to the books,'' he said.

''If you dig a little bit, you see there are big comments about class and racism and power and greed and loneliness - all the most important human emotions.''

Radcliffe has also noticed major differences between Cuaron and his predecessor.

''Alfonso (Cuaron) directs in a more intense way - the scenes in this film are some of the most passionate and emotional I have ever worked on.''

Shrek 2, featuring the voices of Eddie Murphy, Mike Myers and Cameron Diaz, already has broken box-office records in the US ahead of its debut in UK cinemas.

The film, about a green ogre and his donkey sidekick, opens in Britain in July but has received rave reviews in the US, where it took $11.8m ((pounds) 6.6m) at the box office in one day, a record for an animated film.

Playing in a record 4163 US cinemas this weekend, the computer-animated hit is also the first film to have surpassed the 4000-theatre mark on its debut.

WHAT THE CRITICS THINK

''I always thought that a director with more of an indie film background would be better suited to direct these movies. Everything is better - the storytelling, the acting, the music and the special effects.''

A Time Warner employee on www.hpana.com

''As for Cuaron, he makes the film an outright thriller. It starts out light but slowly the creepiness begins to, uh, creep in. For the first time we sense we are in a magical world.''

Red Whale on www.aint-it-cool-news.com

''This is a darker film. The differences between Columbus and Cuaron's directing is night and day.''

Alexandria, a reader of www.the-leaky-cauldron.org

''The movie is great, not fantastic. I would give it five out of six stars. Cuaron has made this franchise worth its name.''

Pim De Kaysergracht on www.aint-it-cool-news.com