It will be very interesting to see how this plays out.
In my area the current yrs 7, 8,9 and 10 were huge bulge years in terms od state places.
If some of the private school children leave not sure there are state places to take them at present. I guess they will have to increase class sizes, they have a duty to educate after all.
For some parents who are working and pay the fees from salary (i.e not banked wealth) the amount they earn over £100k (which is effectively taxed at 60% for £25k and then 45%) is the additional money they need for the school fees.
I can forsee some parents thinking sod it, go state stick the money in the pension pot and not pay the marginal rate of tax.
Other parents will stop spending on other items such as going out for meals, clothes etc. so the govt. might get a few hundred a month more in VAT but it will hurt the economy in other areas.
Other parents will move house and push the prices up near the best state schools. £2k a month per child goes a long way on mortgage.
Others will find god.
Unless Labour are going to scrap faith schools and introduce a lottery system for state allocations the system will be still be unfair, but hang on that won't win votes...