Half-Way House, n. — Green’s Dictionary of Slang

Half-Way House n.

[the volume of mentally disturbed inmates, making it a ‘half-way house to Broadmoor’ (the UK’s main prison for the criminally insane)]

(UK Und.) Parkhurst prison, Isle of Wight.

1939

V. Davis Gentlemen of the Broad Arrows 151: I began to understand why the Island Prison has been termed the Half-Way House to Broadmoor.