Ian McKellen was concerned about The Hobbit shooting schedule

Sir Ian McKellen was worried about signing up to 'The Hobbit' because of the length of filming.

The British actor - who has played bearded wizard Gandalf in the three previous 'Lord of the Rings' movies - was concerned about joining the prequel because he didn't want to be unable to do anything else, and not about the money he would earn from it.

He said: "The deciding negotiation was not about money but about dates. Gandalf is needed on set over the next 18 months but with sizeable breaks when I can work on other projects. My worry that I could not easily escape from Middle Earth was lifted."

However, the 71-year-old star didn't find it an easy decision to come to, as he was concerned the film would not be fun to work on and didn't think people would miss him if he didn't sign up.

Writing on his personal website, he said: "As my agent continued to negotiate with Warner Brothers, I kept wondering was Gandalf what I most wanted to do, more than a new play for instance or indeed a new part?

"Sequels aren't necessarily as rewarding to act in as their originals. Could I let Gandalf go? Would anyone else care if I did?"

He also confirmed he would begin shooting the movie, based on the book by J. R. R. Tolkien in New Zealand on February 21.

'The Hobbit' has had a large number of problems since plans began to be made to shoot it - original director Guillermo del Toro pulled out, and acting unions urged their members to avoid signing up because of contractual issues.