Green’s Dictionary of Slang

scarper n.

an escape, an act of running way.

1888		R. Barnett Police Sergeant C 21 71: What about the other petticoat; the one who has done us all so neat by her beautiful scarper.
1943		R. Llewellyn None But the Lonely Heart 126: The coppers are out there. What would you like to do? Stay here in the hidey-hole for a bit, or do a scarper through the back?
1958		F. Norman Bang To Rights 63: We had all planned to do a scarper.
1978		F. Norman Dead Butler Caper 143: Didn’t wonna take no chance on ’im doin’ a scarper.
1999		D. Looser ‘Boob Jargon’ in NZEJ 13 35: scarper n. An escape.

In phrases

do a Johnny scarper (v.) (also do a Johnny scarperey)

to run off, to escape.

1875		T. Frost Circus Life and Circus Celebrities 279: To abscond from a place, to evade payment of debts [...] is sometimes called ‘doing a bunk,’ but [...] circus men, more frequently use the phrase, ‘doing a Johnny Scarperey’.
1997		A. Livia et al. Queerly Phrased 93: Escape, to do a Johnny Scarper.