Nicolas Winding Refn was not allowed to meet Charles Bronson in person since he is not from Britain, but was allowed to have two phone calls with him. Tom Hardy met with Bronson several times and the two became good friends. Bronson was impressed with how Hardy managed to get just as muscular as he was and how well he could mimic his own personality and voice. Bronson has stated he believes Hardy was the only person who could play him.
Charles Bronson was not allowed to see the film, but said that if his mother liked it, that would be enough for him. According to Refn, his mother loved it. In 2011 Bronson was finally allowed to see the film and called it "theatrical, creative and brilliant".
The British Prison Officers' Association complained when the film's London premiere was prefaced with a recording by Charles Bronson himself, recorded at HMP Wakefield, where he stated: "I'm proud of this film, because if I drop dead tonight, then I live on. I make no bones about it, I really was... a horrible, violent, nasty man. I'm not proud of it, but I'm not ashamed of it either... See you at the Oscars." It is illegal in the UK to make unauthorized recordings of prison inmates. This recording appears on some DVD-editions.
Bronson is occasionally seen wearing a small pair of shades. These are not an accessory. According to the real-life Bronson, his years in poorly-lit solitary units so damaged his eyesight that he required darkened lenses just to read.
When the real life Charles Bronson was moved to Parkhurst Prison in 1976, he befriended the notorious Kray Twins. Coincidentally enough, Tom Hardy would later portray both of the Kray twins in the film Legend (2015).
Contrary to popular belief, Tom Hardy did not do 2,500 push-ups a day in preparation for the role of Bronson. The confusion and reason for this rumor is that Charlie Bronson (Michael Peterson) himself was the one doing 2,500 push-ups a day around the time Hardy was meeting with him to gather information for the film script. Hardy himself denied this rumor during an interview in late 2009 with Michael Slenke from Interview Magazine. The full interview is available at the magazine's website. The interview is titled 'Rough Character'.