Green’s Dictionary of Slang

bollocko adj.

naked.

1977		D. Powis Signs of Crime 174: Bollocko Naked : ‘There he was bollocko.’.
2000		N. Griffiths Grits 281: A suddenly realise tharram in the nud, fuckin bollocko like.
2001		K. Sampson Outlaws (ms.) 76: Paul, who’s just been standing there bollocko, wanking himself off.