Ed Miliband is to try to resist setting out his policy to reduce university tuition fees until the end of the month despite pressure from critics – including university vice-chancellors, the business secretary Vince Cable and some former Labour policy advisers.

After years on the back foot over the Liberal Democrat decision to raise the fees cap, Cable said any Labour plan to reduce tuition fees from £9,000 to £6,000 would mean redundancies, larger class sizes and an end to record levels of university applications.

Miliband made a promise to end tuition fees one of the defining issues of his leadership bid and has repeatedly said his ambition is to cut the level of fees to £6,000, but he has yet to find a way to fund the cut that satisfies the shadow chancellor Ed Balls.

Nevertheless, Balls, speaking on BBC Radio 4’s Today programme, said he would not accept the status quo. He said: “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.”

Labour points to research by the Institute for Fiscal Studies that suggests although the system delays payment for education until later in life and is income-contingent, the average debt per student will be more than £44,000 through a combination of fee and maintenance loans.

The business department select committee says the government now acknowledges that the rate of non-repayment of loans will reach 45%, and that may rise. In crude terms, for every £100 the government lends, it gets only £55 back. That has huge implications for the government’s long-term budgeting.

University vice-chancellors went public with their concerns after months of backstage lobbying, warning that such a cut was implausible since it would cost £10bn over a parliament if the government was not to load the cost on to universities.

Writing on the Guardian website, Cable rounded on Miliband, saying: “What Labour is floating sounds like an unworkable policy based on a soundbite, which would leave a costly black hole in university funding. We looked in forensic detail at proposals like Labour’s and found that, in practice, they simply don’t work”.

He said one solution suggested, a graduate tax levied on higher earners, would lead to a black hole in public finances.

He pointed out: “Under Labour’s proposals the income only comes in 10 or 20 years later, when the next generation of graduates reaches peak earnings – leaving a huge black hole in our finances in the meantime. There is an enormous cash flow problem for universities. How does Labour propose to plug this gap?”

He adds: “Another idea being floated to reduce the cost would be to confine the £6,000 to science and technology degrees. This would have disastrous consequences since these are relatively costly courses to provide, and the effect of the policy would be a severe reduction in science and technology courses offered by universities.”

Balls will also be aware that any proposals that do not stand up to scrutiny will be attacked by Labour defenders of the UK universities system such as Lord Mandelson, the former business secretary.

The repeated delays have caused frustration on the Labour side. Mark Leach, policy adviser to Shabana Mahmood who held the universities brief for Labour until October 2013 – wrote on a blog: “I never imagined that we’d be without clarity of the position this close to the election. Although we’ve been gradually understanding more about the problems with the current system since 2010, the basic facts have not changed, meaning that this was always more a matter of political judgment. And every day that judgment was delayed, Labour’s options were limited further.”

Leach predicts Labour will announce a review aiming for a graduate tax in the medium term with a headline promise of a £6,000 limit for those students that stay at home or go on to a two-year course.