The UK has returned to social stratification almost impossible for a non-wealthy child to overcome.

I conjecture that part of the cause is that the Labour Party ceased, over 20 years ago, to try to represent the working class. When rich people encouraged changes to ensure their children would dominate other children, no one had the power to prevent it.

However, industrial globalization probably contributed too.

A similar development has occurred in the US, but some details are different. For instance, it is based on wealth rather than class.