Cockney, originally used as a pejorative term for all city-dwellers, is now used to refer to all the working-class people in London’s East End. It traditionally refers to the accent of English spoken by the working-class population of London, and it became known as Estuary English. Some of the common features of this accent are the glottal stop, substituting a /w/ for /l/, dropping the /h/ for the /a/ in words, and the rhyming slang.
However, studies have now shown that in London’s East End some traditional features of cockney have been displaced by a Jamaican Creole-influenced variety popular among young Londoners known as ‘Jafaican’, also referred to as Multi-Cultural London English. But features of the cockney such as the double negatives, rhyming slang, and the glottal stop are still in use. Other features of cockney also include: the raised vowel in words like ‘trap’ and ‘cat’ so these sound like ‘trep’ and ‘cet’; non-rhoticity, meaning the ‘r’ at the end of words isn’t pronounced; trap-bath split, meaning that certain ‘a’ words like ‘bath’, ‘can’t’, ‘dance’, are pronounced with the broad-a in ‘father’; and th-fronting.
These videos from the British TV show “Mind Your Language” provide some examples of cockney rhyming slang.
This is a cockney slang speech example: