I used to think the graduate tax was a sensible idea, but honestly I now think it's kinda sinister (and yes our current system is basically a graduate tax in disguise).

The idea is that an extra tax should be levied on those who use a public service more. Stop and think about that for a second, is that not against the whole concept of progressive taxation? Should we also levy a tax on people who use the NHS more?

Should a graduate really have a higher tax rate than a non-graduate who earns the same or even possibly more? Should a 40 year old graduate pay a lower tax rate than a 20 year old graduate, because they won the chronological lottery? Plus on a social level, does this not discourage people from low paying jobs that need degrees, such as teaching?

If you are worried that well off people might benefit more from a universal benefit well there's a solution to that: more progressive taxation. The solution to wealthy people benefiting from something is to tax wealthy people more, not use education as an imperfect proxy for wealth.