Looking at my own family, we have one child and, having worked in state education for many years, considered independent education for her when she starts school. Our salaries, if we continue to work full time and climb the ladder, would JUST cover it, there would be very little left over.
However, the concept of a 15-20% rise means there's no way we can afford it and we won't be putting her in if there is a risk we will have to withdraw her later. We cannot "absorb the cost" as the extra money is simply not there. If we're not paying for private education, we'll probably reduce our working hours to enable us to do more supplementary activities with her.
So, thats:
£8000 pa for her education in the state system
£2000 in reduced payments of income tax due to reducing hours
We were considering a small independent which would be likely to close if the number of pupils drops. Several of the teachers we spoke to said they would not return to the state sector under any circumstances, so they will then be job hunting, likely to take a pay cut or be out of work altogether. That's another swathe of income tax.
This scheme will not only cost a fortune and make very little back, it will also make independent schools the preserve only of the super-rich and price middle class people out completely.