My good friend @drleehw pointed me in the direction of this Student Fee Repayment calculator. It's as horrific as it sounds: even given a fair economic wind - which we currently don't have - you'll only every pay back your debt if you start on a massive salary and get huge pay rises all the way through.
And that's not all: the better paid you are, the less you'll have to pay back. So all those low-paying jobs which require degrees (primary teacher, nurse, social worker) or which require further years of qualifications (librarian, researcher etc.) will now be totally unthinkable. Why would anyone not qualified for sainthood deliberately take a fulfilling but frugal post if it means handing more money to the government than a lawyer or hedge fund trader, and without the prospect of ever paying it all back?