There's a little bit of nonsense
being spoken here about how the word cop came to be used as a name for policeman
The word actually derives from the word 'cap' used in Scotland and the North of England and was used to mean 'arrest' ie: 'Cap him, Sir!'
By the 18th century, across the whole of the North, this had transformed itself into 'cop'. Soon in was standard slang for 'policeman'.
This has to be true because I read it in The Daily Telegraph.