Green’s Dictionary of Slang

1. asleep, unconscious, exhausted; dead.

1929		‘Henry Green’ Living (1978) 221: But ’is son up and knocked him spark out.
1936		J. Curtis Gilt Kid 51: [She] was drunk, proper lit up and had passed spark out.
1952		M. Allingham Tiger in the Smoke (1978) 141: He’s spark out, only just breathin’.
1962		R. Cook Crust on its Uppers 27: The next morning, while we were still spark out with the worst hangover on earth [...] there was a phone call.
1978		F. Norman Dead Butler Caper 125: I [...] went spark out the moment my head touched the pillow.
1985		J. Sullivan ‘Sleeping Dogs Lie’ Only Fools and Horses [TV script] I thought that when I saw him spark out in the back of the van!
1998		Guardian Sport 2 Oct. 16: A nice sharp right-hander on the chin, send him piss over teakettles, spark out on the greensward.
2008		A. Wheatle Dirty South 180: I didn’t want my last image of Noel to be of him sparked out on the concrete.

2. rendered incapable by drug use.

2000

J.J. Connolly Layer Cake 165: The kid’s spark out, shot away, tell ya anything.