Earlier quoted context omitted.
It's actually better to think of the UK loans as a graduate tax - and in that way it's pretty progressive. You pay 9% extra from when you earn over 25k a year (IIRC). So those who need a degree to go into lower paying, yet skilled, professions (nursing, teaching) can do so easily safe in the knowledge that yes, there's this big sum of money that they "owe" but it'll only be taken once they are earning an OK salary, a…
If you make 50k, have a child, and have a student loan, your marginal tax rate becomes 62%, that's 40% (income) +2% (NI) +9% (Loan) + 11% (child benefit reduction). I don't think that's progressive, I think it's excessive taxation.
Slight correction - if you earn between 50,001 an 60,000 you lose child benefit, if you're on 50k you keep it all.