...ANY BLOKE WHO LIVES IN LONDON IS KNOWN AS A COCKNEY...

Strictly speaking a Cockney is someone born within the sound of Bow Bells. That's St. Mary Le Bow in cheapside and not the town of Bow further East.

Back slang is used by Butchers and to a lesser extent grocers and is still a secret language.

Rhyming slang was originally used in the building trade and has now become widespread with new words being added all the time. It is quite in order to make up one of your own and let people guess the meaning.