Matthew Macfadyen was interviewed by the Radio Times for the currently airing The Enfield Haunting on Sky Living. It's a lovely article that has been grossly misrepresented by many news organizations, especially by the trashy Daily Mail.
In the article, Matthew describes how he prefers not to be typecast, especially since some of his earlier roles, including his part as Tom Quinn in Spooks and Mr Darcy in the 2005 film Pride & Prejudice, were typecasting him. He prefers being an actor, not a screen hunk.
Matthew goes on to describe how director Joe Wright backed Matthew for the role of Darcy, as a manly man, while at the same time the studio wanted to beef him up as more of hunk. He feels there is a bit of vanity in hitting the gym to portay a role, when the toning from the gym doesn't portray the role realistically. Darcy would never have a six-pack abdomen, instead he'd be fit from all of the riding he did.
I strongly encourage you to grab the current issue of the Radio Times.