A DARKER plot and more sinister goings-on are in store for the third film adaptation of J K Rowling's Harry Potter and the Prisoner Azkaban when Harry, Ron and Hermione return to Hogwarts for a new term.

Credited with creating the darkness in the film is director, Alfonso Cuaron, who has taken over this time from Chris Columbus, who directed the first two adaptations.

Alfonso says: "From the moment I read the book I knew it was something I could be involved in.

"Even though, on the surface, this is a story about magic and magical creatures, it was the issues explored in it that were so interesting to me."

The acclaimed writer-director, who was nominated for a Best Screenplay Oscar last year for Y Tu Mam Tambin, says: "It deals with issues about growing up, identity, relationships with friends, the lack of parental guidance and the search within. There are also issues about social class, injustice, racism things that affect all of us around the world."

He adds: "I was very lucky as I inherited a universe that had already been created by Chris Columbus.

"He started everything off. It is like building a kitchen. He built everything, got all the ingredients together and decided on the recipes.

"I just had to walk into a ready-made kitchen and start cooking the food."

Having spent a total of four years directing Harry Potter and the Philosophers Stone and Harry Potter and the Chamber of Secrets, Columbus made a decision to take a step back and spend more time with his family.

Chris, who is now one of the producers, says: "Choosing another director to further explore the world of Harry Potter was really a double-edged sword.

"On the one hand, we were looking for a director who would be happy to take on an established universe, with sets and a cast already in place, but at the same time we wanted someone who would bring their own point of view and vision to the production.

"We wanted the audience to continue these adventures with the characters and world theyd grown to love, but be equally exposed to a new perspective."

Chris says: "I really needed to get out and spend time with my children. As a producer you get to step back a bit and watch, and it has really been a learning experience working with someone as talented as Alfonso."

For the three young stars of the Harry Potter phenomenon, Daniel Radcliffe, Emma Watson and Rupert Grint, it was a challenge working with a new director.

Daniel, who plays Harry, says: "I got the chance to put into practice everything I learned working with Chris.

"Working with Alfonso was great, and I have learned so much more again."

For Emma Watson, the greatest gift Columbus gave her was confidence, which she says was crucial to her portrayal of Hermione in the Prisoner of Azkaban.

She says: "It has just been great fun. I love playing Hermione, and the Prisoner of Azkaban is my favourite book, my favourite script.

"In this one it's a real turning point for Hermione, she is rock'n' roll, she is girl-power. I love it."

In this third film, escaped convict Sirius Black, the man accused of leading to the murder of Harry Potters parents, is on the run, and rumour has it he is after Harry. To play the part of the sinister wizard, the filmmakers turned to actor Gary Oldman.

Producer David Heyman says: "Gary is one of the finest actors of his generation, and one of the brightest, most sensitive and caring actors Ive ever worked with.

"Whenever you see Gary in a film, he is compelling, dynamic and dangerous, but there is a vulnerability that lies within him.

"These qualities of danger and warmth are vital to the role of Sirius Black, and Gary very powerfully conveys all of the character's emotional complexities."

Daniel Radcliffe was in awe of meeting Oldman before they started filming. He says: "I am such a huge fan of Gary Oldmans, but hes such a cool guy, and he made us feel very comfortable."

Gary adds: "I was just as terrified. I came into this ready-made family where they had all known each other and worked together. I was thrilled to be a part of this family, this phenomenon."

He adds: "I was a superstar overnight in my kids' school when this was announced. They take me to school now on their 'share' day. They love the whole experience."

Another new cast member who joined the family for this latest film was Michael Gambon, who plays Hogwarts headmaster Dumbledore the role left vacant following the death of Richard Harris last year.

Gambon (Sleepy Hollow, Gosford Park, Angels in America) says: "People often ask me what its like to be taking over from Richard Harris and I liken it to King Lear. So many actors have played Lear, and none of us worry about what the previous actor has done, you just take the part and make it your own."

But Gambon does pay tribute to Harris in his own subtle way.

He says: "I am originally Irish, and on my first day of shooting, the Irish accent just came out. It seemed natural, and Alfonso liked it, so I kept it. I think of it as my homage to Richard."