"You'd imagine that my character has been rather deskbound in the past but this time he will get to take part in the action. I can't give the story away as George Lucas would kill me but I have been engaged in far more physical activities than any of the other films.
"I have found myself sliding down chutes at speed and landing on heaps of rubber, it's been a completely new experience for me. I haven't had to go down the gym to get fit for the scenes but I did need a few rehearsals to get up to speed.
"Most of my scenes have been with Anakin Skywalker (played by Hayden Christensen) who eventually becomes Darth Vader."
"But even though I've been in four Star Wars films I'm glad that I don't get mobbed by fans. I try to keep fame in proportion, sometimes people ask me for my autograph but I can still travel on public transport without being bothered and I hope it stays that way."
McDiarmid added that Star Wars: Episode III won't be released for "another 18 months or so". It also stars Ewan McGregor, Natalie Portman, Christopher Lee and Samuel L Jackson.
He went on: "There's a lot of anticipation about the movie and I think it will be worth the wait."
Thanks to CS! for the heads up!