First of all London is not England or the UK.Try almost any of the supposed 'slang' on anyone from outside the area and you shall be not understood or even thought insulting. Most of the slang which is genuine rhyming slang is confined to quite a narrow band of people; the traditional London working class and their descendants who live to the East of London, along the Thames Estuary.Some of it travels over time so it becomes widely used . 'Have a butcher's' is said by non-Londoners (e.g Fred Puli
). It means 'take a look' : "Is that our cab outside? Have a butcher's" " Take a butcher's at the new paintwork and see what you think" [Butcher's: 'butcher's hook', look ]
These sites and books of 'cockney' or 'rhyming slang' are devised for tourists and non-Britons. Little of what they contain ever occurs outside the imagination of the writers.
Of the links given only the Oxford link; the link to the compilers of the Oxford English Dictionary; and the link 'Londonslang' are of any value. You'll notice that the latter has many 'suggestions'. Some of these are undoubtedly overheards but many are just that, by the sound of it, suggestions for new slang. For example 'bunny boiler' is commonly used nowadays in much of the metropolis: an example not of rhyme but of cultural reference, which much of our slang is throughout Britain.
The slang as used , if rhyming, never contains the rhyme word .Any worked example of slang containing it is fake or, just possibly, the speaker has never heard it used in life. Old Londoners still say 'apples' for stairs not 'apples and pears', 'whistle' for (a man's) suit ['whistle and flute', supposedly].Our 'butcher's' is a common example.
It is the purely cultural slang which is hardest.It is hard enough when the rhyme is to a name barely known to you but this is almost impossible for the stranger .Last year I heard someone answer a question " Cough !" his friend said " Are you sure?" and got the reply " Double cough!". This was a reference to a notorious cheat on the "Who Wants to be a Millionaire" quiz. His accomplice was in the audience and signalled the correct reply by coughing at the appropriate point;one cough was for the correct choice in the multiple choice answers, the double cough was when the contestant wavered . This year this slang for 'yes' and 'most definitely' has died out.
Other culture- based ones become popular and permanent. Even non-Londoners sometimes call the police 'Bill', a reference to the worldly, suspicious and cynical old soldier 'Old Bill'in a WWI cartoon series. Old Londoners still, correctly, say 'Old Bill': " Careful, Old Bill will hear us". 'Sweet F.A'. is another . It means [bitterly] 'nothing at all': "What did he bring you for your birthday?" "Sweet F A !" . It is not abbreviated, vulgar, 'Anglo Saxon' ".....all !" but 'Sweet Fanny Adams' a victim of a C19 child murderer who left the body in pieces spread around . It was reputedly not recognisable or identifiable as a body any more; there was, in effect, nothing left.
There is no such thing as a cockney, by the way. Londoners only ever refer to themselves as cockneys when they are talking to foreigners and outsiders, for whom it is widely understood as meaning 'of London' or even 'English'. Of themselves they are "from North/South of the River" or "North/South/ East/West Londoners"
