Green’s Dictionary of Slang

1. a tramp.

1978		G. Isaacs [title] Leggo Beast Dub.
1980		(con. 1950s) M. Thelwell Harder They Come 16: I nah bring you up like no leggo beast.
1981		N. Farki Countryman Karl Black 60: Him is like leggo beast in the district.

2. a person, usu. a woman, with loose morals; by ext. a prostitute.

1999		(con. 1979–80) A. Wheatle Brixton Rock (2004) 77: You and that leggobeast were so tight, you has a print of her knickers on your Farah’s.
2001		(con. 1981) A. Wheatle East of Acre Lane 122: Nuff leggo beast an’ blue foot were always der [...] dem whores who operate from Bedford Hill.