I am state educated myself, and my children were all state educated.
However, I do not have a problem with independent schools, even the most renowned ones, such as Eton, Harrow and WInchester, etc.
Remember, their parents (UK ones) have already paid taxes, but choose not to avail themselves of the state education on offer, and pay extra to have their children educated privately.
It seems there are mainly 3 ways this could happen.
a). You could abolish the charitable status, and charge VAT. However, I understand this already applies to lots of private school, so no change there then.
b). You could close the schools, sequester the buildings, facilities and land, and redistribute the students to other state schools. Apart from the overseas students, many of the UK students will be boarders (parents in the military overseas, etc). Assuming sufficient notice was given, the overseas students would probably move to schools abroad,(thus losing the UK income) but it also assumes that there would be sufficient places in state schools for the extra UK children. Taxes would have to increase to pay for them.
c) Somehow nationalise the school, keeping the buildings facilities and staff, but make them into state schools. (Taking over their endowments, etc).
[Note An earlier poster said this could apply on a year by year basis. So, all new year are state education, etc. This would create practical difficulties of part private and part state education].
Nationalising the entire school, assumes that the school, staff, facilities, are static commodities to be acquired at will. In reality, some facilities are static (buildings swimming pools, tennis courts), some facilities will be moveable (trampolines, sports equipment, books). It also assumes the staff (and students) would not have a choice.
Many of the buildings are historic and have Listed status, and would require extensive remodelling to accommodate the larger class sizes.
Options b and c, run into so many legal difficulties, that I do not think it would ever happen.
If we assume that somehow all private schools would cease, the smaller ones would obviously close, but the most renowned ones, would move abroad.
As an earlier poster said, all the rich parents would ‘colonise’ a local ‘rich’ area, and squeeze out the poorer children, so their ‘state’ schools, would still be better resourced, even if they came under state control.
It is also impossible to prevent additional private tuition.
So, my view has always been, that the real answer is to make state education such, that fewer parents would opt to send their children private.