"Those mid-high income families barely scraping by to put their kids into private will pull them out and spend the money on buying houses near the best state schools/grammar schools making it impossible for those on a lower income to afford to live within catchment."
What percentage of middle class families with children at fee paying schools will no longer be able to send them there because they won't be able to find an extra £7 a day to cover the cost of VAT. (working on the assumption that private schools won't be able to cut costs to absorb VAT - obviously state schools can cut costs, just not private schools with twice as many staff per child). Show us your working out - link us to the evidence you've seen on the incomes of people with children at fee paying schools.
"State schools will become oversubscribed when families pull their kids from private and the catchment areas made smaller, so only those who can afford to live very close to the good schools will be able to get in."
My children's school uses fair banding and lottery selection to address this issue, and this is one way of beginning to address the issue of social selection in state schools. This means that despite it being in a road where there's not a single property is worth less than a million quid, it still provides place for many kids from local council estates. It's not beyond the scope of the government to address selection by postcode and designing admissions policies.
"This trickle down effect will continue. It will take years, but the class & educational divide will become even bigger."
Nope - because even socially selective state schools still only have 7K per child per year. Unlike fee paying schools which are charging 15K per child per year. The biggest inequality is created by the utterly enormous differences in resources between state and private schools.
The best thing that could happen to state schools is for private schools to disappear overnight. That's never going to happen but if anything would motivate people in positions of power and influence in government and the media to improve our state schools is if their own children had to attend them, unlike at present where almost none of them do.