Crabtree was a police officer working in London in 1953.
He and Detective Inspector Bishop were tasked with investigating the mystery of the humans made faceless by the Wire. (TV: The Idiot's Lantern)
Unlike Bishop, Crabtree was plain-clothed, thuggish, and far from talkative. He was also not afraid to use violence; he punched the Doctor, which knocked him out. (TV: The Idiot's Lantern)