The accent that you're talking about is very prevalent in east/south and even north London. I've heard it being called 'Multicultural London English' in formal situations. It's the result of African and Caribbean (and to some extent, Pakistani) accents being mixed with Cockney & Essex & general London accents. The actual content of their speech (i.e., the dialect) is a result of that same mixture. For example, the term 'hard man' is, from what I can understand, used in Nigeria.
It's very common in working class areas. White & Asian people pick up on it too.
However, holding on to old forms of English and rejecting change does nobody any good. Speaking in a manner that is widely understood is good - but slang doesn't harm that. The world has changed a lot since the Standard English we speak today was formed. Ideally, language should be constantly developing to keep up with our constantly developing society. Cringing at the word 'selfie' does nobody any good. It's a word that we need to describe a concept that already exists. Trying to appeal to a snooty crowd of elitists that hate change (read as: retain prejudiced values that were even more prevalent fifty years ago than they are now) is pointless. If you look back at all the old 'classics' dusty academics revere, the writers who are now praised for their wordplay (for example, Shakespeare and Chaucer) often did not care about trying to adhere to traditions or 'the good old ways', or 'proper' ways of speaking and behaving. Sticking to something outdated prevents topicality and greatly hinders writing. They spoke in a language that the working class could understand, and used slang that the working class could understand.If we constantly criticise any accent or language developed by the working class and cling to everything rich intellectuals say, we're discrediting ourselves (or rather, we're discrediting the working class).