Green’s Dictionary of Slang

a policeman.

1879		‘Autobiog. of a Thief’ in Macmillan’s Mag. (London) XL 500: All this time I had escaped the attention of the reelers (police), but one day I was taken for robbing a baker’s cart.
1884		Ally Sloper’s Half Holiday 7 June 47/2: To others Samuel Hardstaff is a peeler, a reeler, a copper, a Bobby, a Robert, an unboiled lobster, or a slop, but to cook he is Mr Policeman.
1884		Wkly Freeman’s Jrnl 20 Dec. 7/6: I was jogging down a blooming slum in the Chapel when I butted a reeler who was sporting a red slang. I broke off his jerry and boned the clock.
1887		‘Dagonet’ ‘A Plank Bed Ballad’ in Referee 12 Feb. n.p.: I saw as a reeler was roasting me brown, / And he rapped, ‘I shall just turn you over.’.
1904		Sun (NY) 10 July 29/4: Here is a genuine letter written in thieves’ slang, recently found by the English police [...] The noise of the milling the glass brought tray flies. She chucked a reeler and was lugged before the beak and fine[d] a bull.