Ed Balls, the shadow chancellor, has been unable to guarantee that Labour would protect university funding, as vice-chancellors warned the party’s plans to reduce the tuition fees cap would affect the standard of higher education.

Balls attacked the status quo, a £9,000-a-year tuition cap, which he pointed out is just as expensive to the taxpayer as the system it replaced and is storing up problems for the future.

He said George Osborne, the chancellor, is playing “fast and loose” with public finances by pretending the system is working.

“The universities are hugely important but the status quo is not working well at the moment for the students, for taxpayers and the government for a clear reason,” he told the BBC Radio 4’s Today programme.

“We were told that the increase in fees to £9,000 would save money for taxpayers, save billions and deliver a good deal. What we’ve seen is graduate contributions go up by over 50%, graduates paying for their fees, we’ve seen money for universities go up by 28%, but it turns out it’s costing taxpayers more, not less, and the truth is we’re now in a position where almost half of students aren’t repaying fees because they don’t earn enough in their lifetime … there is a huge looming charge for taxpayers in the future.”

However, he was unable to confirm that universities would not lose money under a new Labour tuition fees system, which is likely to be unveiled later this month.

A reduction to £6,000 a year, thought to be favoured by the Labour leader, Ed Miliband, is estimated to cost an extra £2bn a year.

Ahead of the new policy, vice-chancellors represented by Universities UK warned in a letter to the Times that a lower fee cap would lead to “cuts to universities that would damage the economy, affect the quality of students’ education, and set back work on widening access to higher education”.

In the letter signed by Sir Christopher Snowden, vice-chancellor of the University of Surrey, and English colleagues, they said the move “risks the equality of education for all”.

“Any move to limit the number of students attending universities as a way of reducing costs would remove opportunities for young people and those seeking to return to education, and act as a barrier to economic growth,” it said.

They argued that students would be better off with more financial support for living costs, because they are not having to start repaying their loans until they earn £21,000 a year.

David Laws, the Lib Dem schools minister, said Labour’s proposals were unaffordable.

He said Labour would be “very foolish” to put forward a populist policy that harmed the chances of children from disadvantaged backgrounds.