I have lost my "cuntree" accent, because that shit is a far bigger impediment to getting a job than actual class. (and in some cases race, but thats more complex)
but, for those who are outside of the UK and want to understand, its hard to translate. There are three things that you are judged on here in the UK, and they are all sort of related to class:
o Your clothes
o your attitude
o your accent
All of these are proxies for class. The most important thing to be aware of is that race is not normally a signifier for class. to use a recent example:
Rishi, our new prime minister, is posh as fuck. Posher, but not by much, than Liz truss. However less posh than Boris, as he is a no fooling aristocrat.
If we compare Rishi to Priti Patel, former Home secretary, who is middle-middle class at best. The differentiator is accent, not wealth. Rishi is richer than the king, but thats not why he's posh.
That is not to say that race is not a factor. its just nowhere near as big of a thing as it is in america.
The advantage is that you can change your class, its much harder to change your race. However your class at the time of your birth leaves an inprint/set of habits that are difficult to overcome. I do know someone who was raised on a london estate with a strong SAAAAAF LAAANDEN accent, who now is a QC/KC (senior lawyer) and has a received pronunciation accent. It wasnt until I met her parents and sister that I realised how much she'd changed.
[1] https://youtu.be/Feb-CdHBXc8?t=114 Although the mum has quite a soft central norfolk possibly norwich accent.