Apparently we should look forward to a new plan from Labour on university funding this month – if its leadership team can agree on it. The Labour plans for “£6,000 tuition fees”, anticipated in a piecemeal fashion in the media over the past few months, seem to be a complex and technically flawed way of helping Ed Miliband to deliver a sound bite for the general election.

As highlighted by the response from vice-chancellors today, universities would most certainly be the big losers. With the publication last Friday of the latest Ucas statistics – showing growing numbers of students going to university – we have a telling and positive scorecard for the impact of this government’s reforms on universities.

So here are the five questions that Labour needs to answer:

1) If it ain’t broke, why try and fix it?

The coalition government took an unpopular but necessary decision earlier in the parliament on university financing. Our aim was to ensure, through tuition fee loans, that universities were properly funded to provide quality teaching, to expand the student population and ensure that any subsequent payment by graduates was progressive – which means based on students’ ability to pay. Liberal Democrat ministers made sure there was generous funding for students from disadvantaged backgrounds and no up-front fees. Our aim was also to ensure substantial savings so that all the burden of spending cuts did not fall on further education and training. We have achieved these objectives.

Our higher education system is now a success story. A strong reputation for quality attracts large numbers of international students who bring in revenue and expertise, and stimulate growth. Despite dire predictions to the contrary, applications to higher education from 18-year-olds are at an all-time high, as are those from disadvantaged students.

2) A populist soundbite – but at what cost?

Around a million students are potentially affected by any change in the fee cap. The obvious flaw in Labour’s proposals is that universities would stand to lose significantly in fee income – estimated to be £10bn over five years – potentially resulting in staff redundancies, bigger classes and inferior teaching. That money also finances more than £700m a year in activities to help disadvantaged students through bursaries and other access measures.

3) Where would the money come from and when?

Earlier Labour proposals such as a bank levy have been overtaken by other priorities. The new solution appears to be a supplementary “graduate tax” on high-earning graduates. The problem here is not the principle – higher-earning graduates should pay more, and indeed do in our current arrangements – but an important practical difficulty. 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?

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.

4) How does Labour propose to collect a graduate tax from EU students and UK graduates living overseas?

This is another very tricky problem with a graduate tax of the kind Labour is apparently proposing. How is it to be extracted from the many thousands of EU students who come to English universities – almost 43,000 students from mainland Europe have applied in 2015 already – and who go on to pay up to £9,000? Under the fee-loan system it is possible to enforce the debt, and we do, from graduates who return to Germany, France or wherever. There is however no mechanism for applying a new tax across the EU. Nor is it possible under EU law to discriminate by taxing British graduates but charging fee loans to continentals. Under Labour’s proposals British taxpayers would have to subsidise EU students to study at English universities

5) Why is Labour making regressive changes that benefit higher earning graduates before lower earners?

We deliberately set up the loan system so graduates on lower incomes would not have to pay it back in full. We did not want loans to act as a disincentive to study. However, the proposals floated by Labour would do the opposite: those who benefit from cutting fees are richer graduates. In 2010 my colleagues and I devised a policy that protected universities and students, especially the poorest.

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.