Bert, rto be fair, in my absolutist utopia, they could go to a state school but only where a space was available once all state-educated pupils had been allocated places - ie like a current in-year or late applicant.
So in a grammar school situation, they would get a place if not all places were filled by state school applicants, or they would get an occasional place out of year if there were no state school applicants for it.
This would be the same for transferring to a state comprehensive - if there was a place, and no waiting list, someone needing to transfer from a private school could do so.
the whole point is that my proposal is designed to ensure that all children EXCEPT those whose parents can, from the outset, guarantee funding for 'cradle to grave' private education (and consider the higher university fees worth it) attend state schools.
Then it ensures that every school has a socio-economic and SEN mix statistically matched to the wider area it is situated in (local authority area, to a first approximation), through use of differing effective catchments.
However, i agree that this is an absolutist view.