Green’s Dictionary of Slang

an alcoholic; also attrib.

1965		L. Haylen Big Red 153: He’s an ‘alco’ — a rumpot.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 17: Alko Alcoholic.
1993		R. Doyle Paddy Clarke Ha Ha Ha 169: Shut up; your da’s an alco.
1996		J. Murphy A Picture of Paradise in McGuinness Dazzling Dark (1996) Act II: Down and out, on the streets, must be an alco.
2012		(con. 1980s) I. Welsh Skagboys 439: Begbie, wi an alco jailbird father.
2018		I. Welsh Dead Man’s Trousers [13]: — Disgraced alco cop suicide, ah explain tae the cunt.