wrt to a salary sacrifice - well if you've been earning prior to starting a sacrifice scheme then you're going to find yourself worse off.
A graduate isn't. They're going to see an additional deduction on their payslip. This idea that they're somehow going to have a huge debt over their heads for life is fantasy. if they're earning x a month and then found themselves It's monopoly money - numbers on a statement there that move to a statement here. The graduate in question never actually sees the money to miss it.
Look, when looking at a job you see a gross pa figure. There's all kinds of deductions that get made to that figure before it gets turned to the net payment figure. Tax / NI, salary sacrifice schemes, pensions, sharesaves, etc etc. This is simply one more deduction with the bonus that it might stop in the future.
It isn't debt. You're not going to have the baliffs at your door if you can't pay it, it won't impact on your ability to get a mortgage or a credit card.
Does this mean that the graduate earning £45K pa won't be able to afford a mortgage, family etc? Who knows, "afford" is a very relative term but a graduate on £45K - even with that 9% on the remaining £24K is still going to be miles better off than the non graduate on £25k. Will the on graduate be able to "afford" to start a family and all those other things?
I'll ask again, if this were a graduate tax of 9% for salary over £21K would you still class this as a "debt"?
And as someone else said, I actually agree that this is somewhat regressive - like so many things the poor can rely on state help and the wealthy can afford it. Its those in the middle who will suffer. This is why I support the idea of a graduate tax rather than some convoluted system where an adult is penalised on their parents income.