Green’s Dictionary of Slang

(UK Und./police) penal servitude.

1881		Newcastle Courant 2 Dec. 6/6: Bill got ‘seven years pinnals’.
1884		Leicester Chron. 26 July 12/1: [He would] be copped and have another dose of penal.
1907		D. Stewart Shadows of the Night in Illus. Police News 19 Oct. 12/1: ‘You’ll have a tidy spell of penal before you’.
1910		‘Doss Chiderdoss’ ‘Poetry in Prosaic Places’ Sporting Times 19 Feb. 3/2: Three years’ penal left the poet calm, unruffled by the shock, / For great thoughts make even prison life sublime.
1925		E. Jervis 25 Years in Six Prisons 39: The other is doing his fourth lot of ‘penal’.
1941		V. Davis Phenomena in Crime 179: The notorious ‘shadow’ got seven years penal.