Green’s Dictionary of Slang

the Flying Squad; thus sweenies, members of the Flying Squad; also attrib.

1936		J. Curtis Gilt Kid 223: Coming along in a jam jar too. That made them look like Sweenies.
1938		F.D. Sharpe Sharpe of the Flying Squad 333: sweeney todd (the) : The Flying Squad.
1938		J. Curtis They Drive by Night 83: If the Sweeny car did stop for running the rule over the lorry what was the best thing?
1955		(ref. to WW2) B. Hill Boss of Britain’s Underworld 98: He is now a Superintendant [...] In those days he was an Inspector on the Sweeney.
1969		S.T. Kendall Up the Frog.
1977		D. Powis Signs of Crime 203: Sweeney (Todd), the The Flying Squad (named after an apocryphal nineteenth-century criminal barber who butchered his victims and sold their corpses to a meat-pie maker).
1981		P. Wright Cockney Dialect and Sl. 108: ‘Sweeny Todd’ [...] means ‘flying-squad’.
2002		D. Shaw ‘Dead Beard’ at www.asstr.org 🌐 Maybe I won’t even wait to get pope in rome before I sound off: maybe I’ll ask the local bottles and stoppers if they know about what’s on your sheet with the sweeny todd.
2016		Vanity Fair 16 Mar. 🌐 The two detectives seemed a far cry from the fabled 1960s and 1970s Flying Squad sleuths known as ‘the Sweeney’ [...] (The expression is Cockney rhyming slang derived from the name of the murderous barber of Fleet Street, ‘Sweeney Todd’).