It was with extraordinary audacity that Damian Green, the immigration minister, last week questioned the value of the UK's international students. His argument that there is "scope for further examination of whether and to what extent foreign student tuition fees boost the UK economy and, crucially, how UK residents ultimately benefit" prompted bewilderment, quickly followed by anger.

There are, after all, reams of hard evidence on the subject. Perhaps Mr Green should have read the report produced last June for the Department for Business, Innovation and Skills, with its helpfully explicit title for time-pressed ministers: Estimating the Value to the UK of Education Exports. They are worth ?14.1 billion, a figure that could reach ?26.6 billion by 2025, it judged.

Mr Green's timing was also bemusing. On the day of his Policy Exchange speech, Jo Beall, director of education and society at the government's own international cultural relations champion, the British Council, was at a Whitehall conference disseminating the results of a major co-study with the Economist Intelligence Unit, Impact of Visa Changes on Student Mobility and Outlook for the UK.

It breaks with quangocracy convention in that it pulls few punches. The report concludes that the coalition's tougher post-study employment and English-language requirements, restrictions on visitors bringing dependants to the UK and tighter visa-extension rules will jeopardise the future of key postgraduate disciplines such as engineering and biotechnology by turning away too many students.

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Don't expect the report to have much effect on Mr Green and his Home Office colleagues, for they seem to have little time for inconvenient evidence. The department's own impact assessment of its student-visa policies found that they could cost the UK up to ?3.6 billion.

The Home Affairs Committee called this figure "optimistic", but even with the sugar-coating, it was too bitter a pill to swallow for Theresa May, the home secretary, who dismissed the warnings.

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"We are concerned that the Home Office still does not take evidence-based policy as seriously as it could," the committee said.

So far, the best explanation for this aversion to evidence has come from John Sanders, former principal of the respectable Cavendish College, which has closed under the new regulatory regime that was trumpeted as a way to get rid of the bogus colleges stereotypically found above the high-street kebab shop.

"The government clearly does not care how it reaches its net-migration target," he said.

Stopping overseas students from entering the UK is an easy but inappropriate way for ministers to approach their stated commitment to cut immigration from the hundreds of thousands to the "tens of thousands".

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Universities UK has argued that the coalition should provide a net-migration count that excludes students. This is the way forward: the public does not tend to see international students as immigrants (something accepted by the business secretary, Vince Cable), and they are far too important to be sacrificed as pawns in a poisonous political game.

In his speech, Mr Green called for a change to the "intellectual basis of the immigration debate". A good start would be to study the evidence and accept the extraordinary financial, social and cultural value of foreign students - but you can't have an intellectual debate with your head buried in the sand.

phil.baty@tsleducation.com.