The comedian initially thought Radcliffe would by the ideal person to bring My Booky Wook to the big screen.
However, he said he changed his mind when he realised what the part entailed, telling The Mirror: "I thought he wouldn't be able to take all the drink. Or the drugs or fraternising with women. So I thought I should do it."
He added that Oasis rocker Noel Gallagher was in talks to appear as a "seedy homosexual" in the film, which is scheduled to begin shooting this summer.
He said: "[Noel] will be a sexually androgynous, amorphous character - it'll be mad. I was speaking to him about it yesterday, and hopefully it'll be great."
David Walliams is also being lined up to play himself, while Brand is determined to persuade Michael Palin to star as a vindictive headmaster.
Talking about the rest of the cast, he said: "I'm going to hand-pick the ladies. It is difficult doing those sex scenes though - it's very awkward. I feel like I really ought to put on a gold medal display of sexual moves."
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