Cockney is a very influential accent. Its present popularity overlaps with the Received Pronunciation loss in usage. These two facts create a situation where RP is “forced” to adopt some Cockney features to maintain its position. In other words RP-speakers prefer to add some non-standard element to their pronunciation in order not to sound too “posh”. It has been happening for hundreds of years, but now it appears to be more intensive. J. C. Wells is of a very similar opinion:
I could say that Cockney is the most important source of the new pronunciations coming in, and this is something that isn’t just today but has been the case for five hundred years. What typically seems to happen is that some new pronunciation arises in Cockney, it’s condemned as vulgar, but then after a time, it comes up-market, people start imitating it, and in due course it becomes Received Pronunciation, and then a bit later it becomes old-fashioned and disappears. And so we have a constant change going on over the centuries. There’s evidence, for example, that the [e?] vowel in “face” was [‘f?:s] and there was the Great Vowel Shift and it became [‘fe:s] and that monophthong, [‘fe:s] which you still get in Scotland and places, gave way to a diphthong [e?] giving [‘fe?s]. And that was originally a Cockney vulgarism, but meanwhile it’s become posh and it’s now the RP form. Cockney has had another innovation and moved on to [‘f??s] and that’s today’s vulgarism. Maybe in another two hundred years the posh form would be [‘f??s]and the Cockney vulgarism would be something else again, I don’t know, [‘f??s].
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