Green’s Dictionary of Slang

Bill, the n.

also Bill
[ety. unknown; ? abbr. Old Bill n. (1). There is a poss. semantic link to beak n.1 (1), but in reality it is unlikely]

the police; thus Bill from the Hill, officers serving at Notting Hill police station in London W11.

[UK]P. Theroux Family Arsenal 230: ‘Eyes front,’ said Murf. ‘It’s Bill’. A policeman in a helmet [...] was coming towards them.
[UK]D. Powis Signs of Crime 173: Bill, or Old Bill Specifically, the Metropolitan Police and, generally, all police: ‘Is he Bill?’ means ‘Is he a police officer?’ [Ibid.] 173: Bill from the Hill, a Specifically, a Notting Hill police officer (once a very busy and active police station) and generally a very energetic policeman.
[UK]A. Payne ‘Get Daley!’ Minder [TV script] 64: If the Bill pull Keith through Daley there’s no come back to us.
[UK]J. Cameron Vinnie Got Blown Away 7: Bill coming in from home on overtime.
[UK]K. Lette Mad Cows 24: The Bill have got their nuts in a knot over LA-style ‘girlz’n’hood’ gangs.
[UK]J. Hawes Dead Long Enough 302: Oh shit, just to see the Bill get a proper pasting for once.
[UK]Observer Crime 27 Apr. 25: [article title] The Bill? This is More Like the Office.

In compounds