Posh means upper class. In British English, long vowel sounds (bath- said like 'barth'), and fewer reduced sounds are often used by posh speakers.
Cockneys are the people of the East End of London, who have a strong and distinctive dialect, with many grammatical variations from standard English and a slang that is their own. For their slang, we have a glossary in our Members Area (registration required) http://www.usingenglish.com/members/idioms/.
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