Downs, the, n. — Green’s Dictionary of Slang

Downs, the n.

[the site of the prison in the fields that surrounded and were geographically lower than Tothill]

(UK Und.) Tothill Fields Prison.

1856		H. Mayhew Great World of London II 82: The cant or thieves’ names for several London prisons or ‘sturbons’ [...] is as follows:- [...] House of Correction, Tothill Fields ... The Downs.
1865		Leaves from Diary of Celebrated Burglar 43/2: They having one of their ‘stalls pinched’ on suspicion, and sent to the Downs (Tothill-fields prison) for a ‘drag’ (three months).
1873		Sl. Dict.
1902		Globe (London) 25 Nov. 1/5: Newgate was known by its guests as ‘the Gate,’ Tothill Fields as ‘the Downs,’ and Millbank Penitentiary as ‘the Tench’ or ‘the Pen’.