Green’s Dictionary of Slang

(UK tramp) to leave.

1931		E. Blair ‘Hop-Picking Diary’ 19 Sept.–8 Oct. in Complete Works X (1998) 231: Jack off, to . . . to go away.
1935		‘George Orwell’ Clergyman’s Daughter (1986) 103: She jacked off in middle of the night in a motor-car [Ibid.] 95: Flo and Charlie would probably ‘jack off’ if they got the chance of a lift back to London.
1961		R. Gover One Hundred Dollar Misunderstanding 20: She likes them jittery tricks cause they pop fast, give her a chance t’jackoff an piss roun.