Green’s Dictionary of Slang

blue devil n.1

also devil in blue
[the blue uniform]

(Aus./UK/US Und.) a policeman.

[US]N.-Y. Eve. Post 21 Aug. 2/1: They shall be driven away by the ‘Blue devils’ to seek pleasure in some other quarter.
[UK] ‘The Chummies’ Society’ in Fun Alive O! 55: A pair of blue devils came in / And hiked us both to the roundakin.
[UK]Duncombe Dens of London 47: A slap on my shoulder, with ‘what do you want there?’ made me turn round; and there I met the ugly mug of a devil in blue.
[UK] ‘Poll Newry, The Dainty Flag-Hopper’ in Gentleman’s Spicey Songster 34: The raw lobsters she sets at defiance, / She tips ’em a bit of her science; / Like a boxer she floors, the blue devils by scores, / And then in a crack she will fly hence.
[Aus]Bell’s Life in Sydney 20 June 3/2: The intervention of a blue devil checked the career of the red fugitive who was consigned to durance.
[UK]Sinks of London Laid Open 44: I laughed at them and still tried it on, when one of them called to a blue devil, ‘Take this fellow into custody.’.
[UK] ‘Wasn’t It Very Polite of Her?’ in Laughing Songster 154: Two lanky blue devils did collar me.
[UK]Yorks. Post 29 Aug. 7/5: The writer substitutes the words ‘policeman’ and ‘police’ for ‘bluebottles’ and ‘blue devils’.