RP remains the voice of authority. Generally speaking, flexibility is the name of the game, as shown in This Life, the BBC series about a group of trainee solicitors sharing a house in South London. In conversation with his superiors he reverts to type and becomes nicely-spoken. This flexibility may be effective, but it signals a big change in the outlook of the upper-middle classes. In the past they wouldn't have had to worry about fitting in with their social inferiors.
All accents are in a constant state of flux, geographically as well as socially.
In parts of London, though, Estuary is mutating into another metropolitan cadence. These young urbanites, many of them white, are talking in the accent of black south London - the Ian Wright version of Cockney. While Estuary sweeps all before it in the South, prejudice about regional accent is alive and well. Of them all, Brummies probably get the worst of it - no wonder they tend to stay in Birmingham. But times move on.