Actor Zac Efron poses as he arrives for the British premiere of Me and Orson Welles at Leicester Square in London, November 18, 2009. REUTERS/Luke MacGregor

U.S. actor Zac Efron takes another step away from the world of high school musicals that made him famous with a part in Me and Orson Welles, which also features British newcomer Christian McKay in the title role.

In the movie, which hits British theatres on December 4, 22-year-old Efron plays a teenaged student who fortuitously stumbles into a minor role in the 1937 Mercury Theater production of Julius Caesar directed by the young Welles.

During one tumultuous week, he makes his Broadway debut, finds romance with an ambitious older woman and dares to cross the overbearing Welles in a coming-of-age tale.

The film is Efron's second release since he graduated from the successful High School Musical franchise which made him a teen idol, after he appeared in 17 Again which came out in April.

I'm definitely sad to see the end of it (High School Musical), but I think it's all about progression and growing and trying new things, Efron told Reuters on the red carpet of the new movie's European premiere in London late on Wednesday.

This is definitely the next step in that journey for me, he added against a noisy backdrop of dozens of screaming fans.

I can't wait for everybody to see this movie and hear their thoughts. Hopefully they can learn something from the film, a little bit about Orson Welles, the history of Broadway. It's pretty fascinating, it's a fun film.

For McKay, being chosen by director Richard Linklater to play the larger-than-life Welles came as a surprise.

We did an old-fashioned screen test together and he (Linklater) never watched it. He was convinced, he said of the casting process.

It would have been much easier to cast a famous star, and when I first met him and he started talking to me about Orson I gave him a list of famous Hollywood stars who could play him.

It would've much easier for Richard to have chosen one of them. He would have gotten the funding easier ... but he stuck with me and that tells you something about the man.

Linklater, known as a maker of cult films like Dazed and Confused and A Scanner Darkly but also with a Hollywood hit under his belt with School of Rock, said he chose Efron for his charisma on screen rather than his star power.

When asked if he feared Efron might overshadow the rest of the cast and the movie itself, he replied:

Not really. I didn't really think about it that way. Selfishly, as a director I wanted to find the best actor I could, someone who could go toe to toe with Orson Welles which is pretty hard to do.

Welles is one of the bigger personalities in the last couple of centuries, so I needed someone with that kind of charisma, with that leading man ... and Zac had that.