This is horribly disingenuous. The figure of £500 is presumably chosen because for many families it's not an utterly unmanageable figure (though equally, for many it is). It's supposed "to fund additional facilities, to bring them into line with those provided in independent schools" and "to increase the number of teachers, so that the class sizes of 34 could be reduced and workload improved for staff". On what planet...?! The difference between funding per pupil in good independent schools (not all have good facilities or small classes!) is way bigger than £500/pupil/year.
So what's the agenda here? If this got accepted, would there then be an expectation that every parent should find that their local state school was offering everything their local independent school was? When that wasn't the case, what then? Increase the price? Arbitrarily? Is this the privatisation of education? OK, if he wants to argue for that, let him do so, but there are huge implications.
The intention seems to be that the money raised goes directly to the individual school. The article makes it sound as though it would be compulsory except for children who attract pupil premium, but I don't believe a word of that. It would end up being voluntary, and so schools would end up being better funded if their parent body was wealthier. Could an argument be made that that's a good thing if it prevents parents who could afford to use independent schools from doing so? Seems a bit of a stretch.
We have a mechanism for funding state schools. It's called tax. We should use it. Everybody benefits from a well-educated population, everybody should be willing to pay for it.