Regular readers of The TES will know that I support the principle of top-up fees for universities. I will not trouble them again with the reasons for my support, which are based on the belief that a service that benefits mainly the children of the middle classes - and is a vehicle for enabling people to move into well-paid professional occupations in the next generation - should be financed as far as possible by its users, not by taxpayers.

I want instead to address what seems to be the fundamental concern of the Labour rebels, what they call the “marketisation” of higher education.

Their objection, as I understand it, is not so much to charging students for courses as to allowing universities to charge different fees.

Each university, the rebels say, is being invited to put a market price on what it offers, and this is wrong. It will lead to “a two-tier system”.

That is why, no matter what concessions ministers offer in the way of more bursaries or grants to poor students and easier repayment terms, many of the rebels will go into the division lobbies against the Government.

Yet we already have a two-tier system - indeed, we have something more like a four or five-tier system. Nobody can seriously pretend that a degree from one of the former polytechnics has the same value as one from Oxford or Cambridge, either in prestige or in enhanced earnings. Students at, say, Luton or Derby or Paisley will not get as much “added value” as those at, say, Bristol or Imperial College or Edinburgh. It is surely unjust, particularly since most of the former come from working-class homes, to charge them the same.

You may argue that instead of striving (not very successfully) to get more working-class students into Oxbridge or Edinburgh, we should get more funds into the Lutons and Paisleys where they are already in attendance. In other words, a Labour government should attack the hierarchy of universities, not support it, just as it once attacked the hierarchy of schools. We should in effect aim for a comprehensive system of higher education.

But I find the idea of comprehensive higher education incoherent. An education that will be available, even under ministers’ most ambitious proposals, to only half the population cannot be comprehensive.

Universities are unique among public services (or private services, for that matter) in selecting their users. Health services, schools, streets, parks, policing and libraries are all available to anybody who wants or needs them. These are areas where the various attempts at marketisation are wrong.

Higher education is different for at least two reasons. First, you should not require taxpayers to pay the lion’s share for a service to which half of them have no access. You can argue, to be sure, that universities deliver significant public benefit in training doctors, teachers, engineers and so on whose services we all use. But we already pay for that benefit (or should do so) through their relatively high salaries.

Second, universities are the only public service where there is a significant international market. The top British universities are already losing academic talent to America where they have higher pay, better research facilities and smaller tutorial loads.

This is why Oxford, Cambridge, Edinburgh, the London colleges and others need urgently to raise more money. Is it seriously suggested that this money should come from public funds at the expense of the Derbys and Paisleys? Or at the expense of nursery schools, further education colleges and hospitals?

Or should we, as the Tories seem to suggest, continue to keep fees low and balance the books by restricting student entry?

Or should the top universities raise the money by taking more overseas students, largely at the expense of British students? Or should we just give up trying to have internationally competitive universities?

On these questions, the Labour rebels are silent.

Peter Wilby is editor of the New Statesman.