Related to Sweeney Todd?

You have the London Met Police.
Within that, you have the Specialist Crime & Operations Section.
Within the SC&O, you have the Flying Squad.
The Flying Squad is nicknamed The Sweeney.

Being London and full of British humour, people just applied a bit of Cockney Rhyming Slang (CRS). CRS isn't actually a separate language or anything and I doubt Cockneys (True ones or otherwise) ever used it in any seriousness. Most people who use it nowadays do so out of fashion, or just because they think it's funny at the time.

Examples:
Apples and Pears - Stairs.
Plates of Meat - Feet.
Dog and Bone - Phone.
China Plate - Mate.
Sweeney Todd - Flying Squad.

Of course, in CRS you'd never speak the whole rhyme. Usually just the first part.
So you'd go up the 'Apples' using your 'Plates', while talking on the 'Dog' to your 'China' in 'The Sweeney'.

There is almost never any actual relation to the rhyme and the word(s) being replaced, aside from the last syllables rhyming.

And there ya go... pretty much the full skinny on WTF these crazy-ass Brits are on about.

It's slang, Sweeney Todd Flying Squad, so you just get The Sweeney.

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