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Wiktionary
mockney

a. Characteristic of a mockney. n. 1 (context uncountable English) An inauthentic imitation of Cockney accent and vocabulary. 2 (context countable English) A person who speaks in this way.

Wikipedia
Mockney

Mockney (a portmanteau of " mock" and " cockney") is an affected accent and form of speech in imitation of cockney or working class London speech, or a person with such an accent. A stereotypical mockney speaker comes from an upper- middle class background.

A person speaking with a mockney accent might adopt cockney pronunciation but retain standard grammatical forms, whereas the genuine cockney speaker uses non-standard forms (e.g. negative concord).