I was trying once to convince a bright working-class white student to become a doctor, because it was what she wanted. She said she would be a nurse because doctors are middle-class and she would become alienated from her family if she became a doctor.
Interestingly, Asian young people have no such cultural problem ,as, generally speakingtheir parents are more ambitious for them. Likewise the Eastern Europeans being educated here.
So yes, the places for grammar schools will be taken by ambitious immigrants and our own middle-class who can pay for prep schools or coaching to gain entrance.