Chatham Pocket means: Anus. The anus is a slang term that’s used in Medway, Kent, south-east England. Chatham is perhaps the most undesirable of the Medway communities. This term is a result of the tendency of local criminals to sneak cigarettes lighters and drugs into police cells by hiding them in their anuses. Chatham’s criminals have a reputation for being so inept they are believed to be able to smuggle cigarettes, lighters and drugs into the police cells. The local police must prepare them by hiding their personal belongings in “Chatham pockets” in order to ensure they stay there. (in Community Dictionary, added by Angeline Schultz)