Image copyright Getty Images Image caption Is a culture of highly selective universities getting in the way of social mobility?

The long-running battle over grammar schools - put back into the deep freeze after the general election result - saw deep-rooted divisions over the impact of dividing pupils by academic ability.

Opponents argued that academic selection really became social selection - and that what appeared to be selection by ability became a filter shaped by social background.

But when it comes to university, it seems that such attitudes are turned on their head.

It's not even even really questioned that higher education should operate on an entry system specifically outlawed in secondary education.

So why shouldn't there be comprehensive universities?

That's the argument put by Tim Blackman, vice-chancellor of Middlesex University, in what Nick Hillman, the influential director of the Higher Education Policy Institute, said was one of the "most thought-provoking papers ever published on UK higher education".

Prof Blackman's contention is that the university system, with its obsession with hierarchies and rankings, has become a barrier to meritocracy.

Instead of driving social mobility, he says, the university system has become a mirror to existing inequalities and is amplifying social segregation.

'Hyper-selection'

At the top are the highest ranking powerhouse universities, Oxford and Cambridge and the leading London institutions, followed by the rest of the Russell Group universities and then down through the ranks of red-bricks, 1960s campuses, middling institutions and then on to the "new universities" that were often former polytechnics.

This is also a system without any real relegation or promotion on merit - as a university group such as the Russell Group can choose who is or isn't a member.

Image copyright Getty Images Image caption Should brighter students be spread more widely throughout the system?

Prof Blackman sees this not as an academic ladder, but a stratified class system.

Even if more young people from disadvantaged families are going to university, there is still a strong pattern of better-off teenagers getting into the highest ranked universities.

He talks of "hyper-selection" at the top of the table, in the scramble for places at the most sought after institutions.

And this creates a system in which a "good" university is likely to be synonymous with being the most selective.

This, says Prof Blackman, is the opposite of what the country needs from a higher education system.

If the UK is blighted with low productivity and a skills gap, he says, what is needed are universities that are strong across the whole range of institutions.

The brightest students should be spread across the system, rather than being clustered in a small number of universities crammed with other similar youngsters.

And he proposes the benefits of a comprehensive university, with a mixed ability intake, making the most of the talent of those who attend - rather than concentrating the prestige, funding and brightest students in a few institutions, to the detriment of the majority.

The analogy used is that a "good" hospital would be one that got the best outcomes for its patients, not the one that started out with the healthiest intake.

'Snobbery'

But even with this radical thinking, Prof Blackman still suggests that there would be an economic argument for a handful of elite institutions - "strategically important world-class research universities".

And it remains easier to identify the flaws in the current system than to propose a practical way of changing it.

Image copyright Getty Images Image caption What should be the purpose of a modern university?

Prof Blackman suggests that the funding system should be shaped to reward universities that create a social mix of students.

But, he says, the current arrangements of high and low status institutions are "based on snobbery and discrimination rather than evidence".

The concept of a non-selective university might seem strange.

It seems to go against the grain of the idea that university is the summit of a journey after getting over a series of tough exams.

But Prof Blackman says the higher education system needs to borrow from the comprehensive principle if it is going to make a difference to social equality and to address the needs of an economy demanding more highly skilled staff.

"The root of these problems is academic selection, which has created a sector based on social class advantages," he says.

The government has tried to shake up the old order in universities somewhat, grading the quality of teaching, in a way that has put some top institutions at the back of the queue.

Universities Minister Jo Johnson said: "Social mobility should be at the heart of our higher education system. This is becoming the case, with more students from disadvantaged backgrounds going to and staying at university than ever before.

"But we know there is more work to do. Soon, all providers - including the most selective - will be required to publish application, drop-out and attainment data by gender, ethnicity and socio-economic background.

"The Teaching Excellence Framework is also refocusing the sector's attention on teaching - putting in place incentives that will raise standards and encourage providers to ensure they are supporting students throughout their studies."