In his speech at the funeral of the Athenian Dead, Pericles famously said that the bravest are those who, while knowing the full strength of the forces ranged against them, still go out and face them. That they do not “faint beforehand with the meditation of future trouble”.

Well, at least we now know what we are facing in preserving our precious international community of scholars and their students. We understand that to speak for our international communities will take yet more courage and resolve.

Last week the Conservative Party published its election manifesto, and it was laid out in black and white. The UK to leave the single market. Immigration to be reduced to the tens of thousands with students included not only within migration statistics but within the scope of its planned reductions. Visa regulations to be tightened. Costs of health for students and employment for overseas scholars to be increased.

As I read it, I thought of all those who had worked so hard to make the case for the importance of international students and staff – not just to our universities, but to our towns and cities, our hospitals, and our economy. And don’t let anyone tell you that we failed to make this case, or that we didn’t work with others, or engage with government, or weren’t positive enough.

In fact, it was just the opposite. More than 100 institutions from our great historic universities to specialist colleges came together to say simply that this country’s higher education is what it is because we are international. We were backed by business groups including the Chambers of Commerce, the Institute of Directors and the CBI. We had a simple message of unity and welcome, told in the voice of students themselves.

As part of a campaign that united UK universities, we commissioned independent research on the net economic impact of students on our city and region. And home and overseas students compiled images and stories of standing together – members of research groups, teachers and students, a poignant photograph of a UK and an Egyptian trainee doctor about to start an early morning shift in a provincial hospital. It came from the head and the heart.

Our films explained the UK visa process by following the experience of students as we travelled to India and China with civil servants from the Home Office to record the process. Such materials became a common resource for potential international students, reassuring them they were welcome in the UK. A Chinese language version was launched in Parliament at an event attended by the immigration minister. The home secretary at the time, Theresa May, had personally approved the collaboration.

And we know that, for its key audience, it worked. The latest Hobsons survey of 27,000 potential international students specifically mentions the role of the #WeAreInternational campaign in making overseas students feel welcome and mitigating fears associated with Brexit.

Yet to assert that “we are international” was never only about recruiting talent to the UK. It was a description of our values, a statement of fact about who we are. It paid tribute to teachers and researchers who make the UK their home and who are our colleagues and friends.

But back to the where we are; the new world laid out before us in the manifesto.

I am undaunted in my commitment to being truly international, and I know that my passion is matched by many of you reading this article. And this passion for an open society that nurtures understanding between peoples is fully matched by many of those in public and commercial life. We are by no means alone, neither in our fears or hopes.

So let’s thank, and stick with, all those who have spoken with us about the international nature of universities and of the contribution we make. Not only the sector bodies and business organisations, or five different select committees and members of the Commons and Lords of all parties who spoke out. Newspapers from Left to Right published facts and even openly campaigned. We must also thank those who made a case and may still be doing so within the government.

And we must let them know that this is too important for us to give up the struggle. We know that UK universities are places of important scholarship and teaching that is crucial to our cities, regions and the world. We know that we are a unique place of meeting and respect between nations. We know that to lose beloved international staff and students could put all that at risk.

But we also know that it will be hard. Damned hard.

International staff and students are naturally sensitive to whether or not they are welcome in a country. In the US of travel bans and political rhetoric about immigration, postgraduate recruitment from overseas is plummeting, with students heading to destinations that are perceived to be more safe and welcoming. The University of Alberta in Canada has seen international student recruitment increase by 82 per cent this year.

In the UK, we have already seen a reduction in the number of talented Indian students following the loss of post-study work entitlements. The Financial Times this week reports the rise of overseas business students in Germany, concerned about post-study visas in the US and the UK. There will be more of this. We must hold government to the idea that UK universities should continue to be the envy of the world and be a first choice for students across the globe.

And when that student, teacher or researcher arrives to be part of our universities, we should make them truly welcome. For a period of time, the UK should be home. As the Hebrew Bible so beautifully puts it: “The stranger who resides with you shall be as a native among you.”

These are serious times in which a new mood in global politics will challenge universities to our core, in the UK and around the world. As a diverse international community, we stand in sharp contrast to a world in which conflict abounds and where hatred may burst on to our streets. Tensions are high. Our freedom to speak as an international community may be sorely tried in the face of a shifting political paradigm.

The issues are fundamental. Who is the stranger? And who is a native? These are the great questions of our age. I must engage with them as a scientist and an educator as much as anyone studying politics or philosophy.

We must do this not least in the memory of those who built our academia, those who kept the faith in more dangerous and trying times than we have had to face. We can and should be a place of hope, of a better way. Some will say that universities really shouldn’t keep talking about immigration, overseas staff and students or internationalisation. Politicians warn that we should end our “dependency” on international staff and students. Train our own Nobel laureates. Give up this selfish strain.

Don’t you believe it. Universities have never needed to assert our values more. To hold fast to the values of global scholarship – and those of humanity beyond academia – is not the response of a spoiled child. It is the courage of our convictions.

Sir Keith Burnett is vice-chancellor of the University of Sheffield and co-founder the #WeAreInternational campaign.