Shadow higher education minister Liam Byrne called on the Tories yesterday to "confess" that raising tuition fees was a disaster after a new study revealed many graduates will never repay their debt.

The Labour MP said the Sutton Trust report proved the £9,000-a-year system is "unsustainable and unfair."

The Trust warned that most graduates will be coughing up loan repayments into their 50s - and three-quarters will never earn enough to clear the debt.

The average amount expected to be wiped out for each student stands at a whopping £30,000.

Mr Byrne urged Universities Minister David Willetts to "confess that this student debt system is not only unsustainable but unfair."

And he asked: "Will he tell us if the Conservative Party has any plans to raise the £9,000 in the next Parliament?"

Mr Willetts insisted: "We've got record numbers of students at university, funding is going to the courses that students choose, we're getting rid of the cap on student numbers and the system is financed by graduates paying back.

"That's the right way to finance our system."

The debate comes after the Star revealed last month that the Tories are considering demands from elite university leaders to scrap the cap on tuition fees completely, risking US-style fees of up to £16,000 at year.

Mr Willetts pointed out that Labour also backs a graduate repayment system.

But a poll of over 700 Labour members for influential website Labour List showed a majority back free education funded through general taxation.

The poll comes just after a day after the National Union of Students conference voted to reinstate a free education policy.