One thing is certain about higher education funding: free tuition means student number controls.

This is because taxpayers do not have bottomless pockets. Finance ministries dislike ¡°demand-driven¡± policies, in which public spending is allowed to float up to the level of consumer demand without any checks. Wherever possible, policymakers limit their financial exposure, and, in higher education, this has generally been done by capping the number of student places. That is how Scotland, for example, continues to pay for free education for home and European Union undergraduates.

But Scotland is an outlier in the UK. Elsewhere, when provided with a choice, voters have opted for more student places and shifting the costs from taxpayers to students via higher fees.

Parties promising to abolish fees in England have had a 100 per cent failure rate in recent times. In 2005, the Conservatives¡¯ then leader Michael Howard promised free higher education and lost. In 2017, Labour leader Jeremy Corbyn did the same and also lost.

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The past is not always a good guide to the future when it comes to predicting which policies will gain traction with the electorate. But it is a guide on one point: if tuition fees were abolished, student number restrictions would not be far behind.

Take Chile, which used to have the highest tuition fees in the world relative to its national wealth. Recent haphazard attempts aimed at moving it towards a free system of higher education have included tight expansion caps.

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Conversely, however, high fees do not guarantee the absence of student number caps. In his autobiography, David Cameron says the reason his coalition government introduced higher fees in England was that he wanted more student places. But this chronology is too neat; in fact, it is plain wrong. Student number controls in England stayed until the autumn of 2015: after the first cohort of students paying the tripled fee of ?9,000 had left university, and after the coalition itself had ended.

Moreover, it now seems likely that student number caps will come back in England whatever happens as a result of this week¡¯s UK general election. This is because even though student number caps are linked to particular student funding models, they have an independent life of their own, too.

There are at least six persuasive reasons why some form of student number cap might be on its way back even if the current high-fee regime were to survive unscathed.

First, it has already happened in Australia, where the higher education system closely resembles the UK¡¯s. Australia removed student number controls in 2012, three years before the UK, but rolled the demand-driven system back five years later, owing, in part, to cost concerns. The free-for-all had suited students, who had more freedom to find the course they wanted, but it proved too costly for taxpayers and politicians to maintain.

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Second, the recent decision to include an estimate of future student loan write-off costs in the UK¡¯s current public spending figures changes the terms of the debate. The cost of the current system of limitless places suddenly looks much greater to anyone who cares about the size of the nation¡¯s deficit, as every Chancellor of the Exchequer does.

Third, the coming explosion in the number of school-leavers, combined with bolder access initiatives and young people¡¯s high aspiration levels, signals a huge expansion in demand. A conservative estimate is that we will need between 300,000 and half a million extra full-time undergraduate places in England over the next decade. That is the sort of financial exposure that gives policymakers the wibbles.

Fourth, as Times Higher Education has exclusively shown, the Conservatives¡¯ manifesto commitment to tackle low-value courses could mean rooting out those that fail a value test (whose details are as yet unspecified). Stopping the funding of courses that you do not like represents a backdoor cap on student numbers.

Fifth, the long-awaited spending review, which will set the future budgets of government departments, could be brutal. The Westminster system is designed to have one general election every five years, whereas we have had three in the past five years. Fiscal discipline has gone out the window and been replaced by election promises ¨C or bribes. But the vice may soon need to be tightened again.

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Sixth, the NHS, childcare and pensions ¨C not to mention the environment and child poverty ¨C all have greater salience than higher education. The same is true of other parts of the education system, such as school funding and, increasingly, further education. As so many people seem to think that university expansion has gone too far, any available resources are less likely to go towards boosting the size of universities than they are to other educational institutions.

English university governing bodies and senior managers currently face unprecedented uncertainty caused by a series of big events, including the election, Brexit and the industrial action over pensions and working conditions. But, however these factors are resolved, no one would be wise to bet on the permanent absence of student number controls.

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Nick Hillman is director of the Higher Education Policy Institute.