Green’s Dictionary of Slang

(UK Und.) a prison.

1624		J. Smith Virginiana in Quinn New American World (1979) 338: To stop the disorders of our disorderly Theeves [...] built a blockhouse .
c.1698		B.E. Dict. Canting Crew n.p.: Block-houses c. Prisons, also Forts upon Rivers.
1725		New Canting Dict.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict. 6: Block houses – prisons.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].
c.1850		Duncombe New and Improved Flash Dict.
1858		A. Mayhew Paved with Gold 266: Just out of the ‘blockhouse’ (gaol) and never felt better.
1859		Matsell Vocabulum.
1881		Trumble Sl. Dict. (1890).
1895		Crowe Aus. Sl. Dict. 9: Block House, a prison.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Blockhouse. Katingal. The term is a visually accurate description of the modern top security prison at Long Bay (NSW) closed soon after being commissioned on humanitarian grounds.