I am often considered ‘posh’, almost entirely because I use Received Pronunciation and live in the north. Speech in this country is significant. I have always spoken the way I do. I don’t do it on purpose.
I think I am middle class, but not the moneyed variety. Both parents were graduates, I was educated at academic private schools (not boarding), but not ones you would have heard of. My senior school took a few pupils who were clever enough to pass the entrance exam, but couldn’t afford the fees. Thus one of my best friends came from a completely working class background - father a docker, no electricity, hot water or bathroom at home. This was in the 1950s. She was very ashamed of where she lived, which I thought was really sad. She is a prime example of social mobility, and I would call her middle class now.
I think we are kidding ourselves, or very unobservant, if we say class doesn’t exist. Of course it does, but I think it is much less important than it used to be.