Cockney English, or "old Earth Cockney", was a variant of the English language, common to residential London, which was spoken by those called "Cockneys".
James Stevens, a journalist, found it difficult to assess Dodo Chaplet's age and origins, as her accent shifted a lot between well-educated Oxbridge tones and a "coarser smattering of Cockney". (PROSE: Who Killed Kennedy)
Drax acquired a Cockney accent while doing time in a Brixton prison after getting arrested for crimes he committed to obtain replacement parts for his TARDIS. (TV: The Armageddon Factor) This trait helped him survive inside the facility and would persist through several of his later incarnations. (AUDIO: The Trouble with Drax)
Cockney master thief Ada Mullins, also known as "the Unicorn", masked her voice in an Oxbridge accent to avoid detection, whilst impersonating Robina Redmond. Once she returned to her 1920s Cockney accent, Mullins used phrases such as "nabbed it" and "it's a fair cop", and negative statements such as, "I ain't no killer." (TV: The Unicorn and the Wasp)
In 5,000,000,023, Cassandra O'Brien.Δ17 attempted an "old Earth Cockney" accent when posing as Rose Tyler, who spoke with a working-class London accent. (TV: New Earth)
The Tenth Doctor spoke in an accent described by George Litefoot as "a kind of cultured cockney flecked with hints of Scots." (AUDIO: The Jago & Litefoot Revival)