IFS say this policy will raise around 5 to 6bn over the course of the Parliament.. 5 years.
That was based on an assumption that any reduction in the number of pupils in independent schools would be balanced by the parents involved spending the money they had saved on school fees on other VATable goods and services. This assumption is, to say the least, questionable. The evidence to date also suggests that IFS underestimated the sensitivity of pupil numbers to increasing prices. They also totally failed to consider the likelihood that some schools would close, leaving some parents without an independent option.
To say again, we don't yet know the effect of this policy. Most parents planning to use independent schools also apply for state school places so that they have a backup option. The fact there has been little change in the numbers applying for state places therefore tells us nothing. We will have a better idea of the impact in September. It is possible that this policy will raise money for the government. It is also possible that it will reduce the government's income.
Everyone wants good public services, but most want someone else to pay. The rich already provide most of the government's income. The amount paid by the rich went up significantly under the Tories, contrary to popular belief. Increasing taxes on the richest often doesn't work. Gordon Brown introduced a top rate of 50% income tax for those earning over £150k. Instead of raising additional revenue, this actually resulted in reduced revenue from these high earners, so the rest of us ended up having to pay more tax to make up the shortfall.