The role of Frank Perry was written specifically for Brian Cox by director Rupert Wyatt, who had worked with Cox before and wanted to work with him again. When Cox refused a supporting role in a movie Wyatt offered him and challenged him to write him a good leading role, Wyatt did exactly that.
Director Rupert Wyatt revealed on the DVD commentary that Damian Lewis wore ladies underwear throughout filming.
WWE wrestler Sheamus and UFC fighter Conor McGregor both appear in this film. (Conor has a non speaking background role)