The student loans repayment system could be a catastrophic time bomb for the Liberal Democrats, Labour has warned, after it emerged nearly half of graduates would never earn enough to repay loans.
Shadow business secretary Chuka Ummuna said the £9,000-a-year fees in England system might end up costing the taxpayer more than the previous tuition fees.
Speaking to BBC One's Andrew Marr Show, he said: "I think this is actually catastrophic, for the Liberal Democrats in particular, because having trebled tuition fees in the name of reducing the deficit and saving the exchequer money, you are are at best seeing it raise little money at all; at worst actually costing more.
"What this is is a student loan time bomb that is actually already exploding under the government."
Danny Alexander, LibDem MP and the government's treasury minister defended himself saying numbers "do move around a lot".
"The figure that we are most pleased with is that we are seeing more people from disadvantaged backgrounds going into higher education than ever before."
Despite pledging to oppose any tuition fee rise at the last election, LibDem MPs supported government legislation to increase tuition fees to £9,000 a year. Vince Cable previously said the public would not believe any political party which claimed it could scrap university fees.
Last year Clegg tried to draw a line under the damaging tuition fees policy u-turn by making a public apology for making a promise he was unable to keep. A video appearance that was famously autotuned and mocked.