Green’s Dictionary of Slang

1. a break from work.

1938

J. Phelan Lifer in DSUE (1984).

2. an escape, a getaway; a getaway driver; thus stoppo driver, a getaway driver; stoppo car, the car in which criminals escape.

1941		implied in take stoppo
1954		J. Phelan Tramp at Anchor 151: I had ‘lamped a stoppo’ — i.e., I had been hoping to escape.
1972		P. Fordham Inside the Und. 23: Tony, a trusted ‘stoppo’, an escape driver. [Ibid.] 35: Skilled burners and a couple of stoppo cars. [Ibid.] 88: The stoppo driver is another highly-rated villain.