Presumably having been promoted beyond the regular uniformed service, he is a very 'laddish' Cop. Intelligent, but rather cynical and pragmatic, his motivation for joining the Force was the 'perks of the job' such as pushing to the front of queues, and (sometimes) using his police status to his own ends.
He is frequently eating or ordering food via telephone whilst on duty. Despite being at Grim's beck and call, he has little respect for his superior and often chuckles at his misfortunes. He provides a comic supporting role similar to PC Gladstone, although his interjections are usually brief "one-liner" stabs. He is paired with female DC Crockett in several scenes (she eventually disappears from the series). Kray is replaced in Series 2 by DC Gary Boyle. Both Kray and Boyle served as intelligent "straight man" characters to the bumbling Grim, not unlike PC Habib's relationship with Fowler.