Green’s Dictionary of Slang

(Irish) drunk.

1970		C. Brown Down All the Days 4: Their father had been drinking since he was twelve, when a pint of stout cost only a penny [...] so that he often got ‘locked’ on a shilling.
1988		R. Doyle Commitments 12: I was fuckin’ locked, said Declan Cuffe. – Rum an’ blacks, yeh know.
1994		(con. 1920s) K.C. Kearns Dublin Tenement Life 63: He’d come in locked drunk.
1996		P. Howard The Joy (2015) [ebook] I’m still not sure if you’d get locked on it [i.e. altar wine].
2005		P. Howard Curious Incident of the Dog in the Nightdress 2: 22:58:04 Residents’ Bor, Berkeley Court, Basically Locked Now.