Green’s Dictionary of Slang

(Scot.) a derog. term for a Roman Catholic; also as adj.

1973		(con. mid-1960s) J. Patrick Glasgow Gang Observed 236: Tim – Roman Catholic.
1994		I. Welsh ‘The Two Philosophers’ in Acid House 116: If the handshake is right he [i.e. a policeman] will let the Billy go and slap the Tim around a bit.
1998		I. Welsh Filth 191: Token Tim bigots who would say that anyway.
2013		T. Black Ringer [ebook] n.p.: If he [i.e. a barman] was a Tim I’d be watching for a gob in the pint; they’ve all had the arse rode off them by priests and not to be trusted.