POGS Crumbs! I have a feeling it is to do with people who come from monied parents having better education, better paid jobs and getting into more influential roles. Conversely, the people coming from humbler backgrounds who don't get the chance for the better education and don't get into the higher roles in the same proportion, are not represented in the influential roles. I hope I've not made that too muddled.
While I'm at it - Grammar schools will only give a better education and better life-chances to a small proportion of children who will grow up to be leaders in their work. Wealthy people will get tuition for their kids to pass the 11+, I've seen it (lived and taught in Kent), or even send child to private crammer before taking 11+. How many ordinary parents will be able to do that? Good comprehensives give respect to everybody and should give the same high educational/academic achievement. It is possible. I have seen it. I have no personal axe to grind. I simply do not want a nation where 90% of people start saying "I failed, I'm not clever, I didn't get to a grammar school" and 90% of our children thinking they are now on the second-best pile and give up their aspirations, identifying themselves as not people who become successful or go to university etc.
How is class measured? It isn't whether you use silver tongues for the sugar cubes in your tea any more. It has to do with level of education, work you do, income bracket, the rest I've forgotten and anyway it's probably different now. It's been used in a lot of health research to useful effect for targeting needs for healthcare.