Belgian law professor Geert van Calster is used to approaches from European students who have abandoned plans to do a PhD in Britain with Brexit looming. But a few weeks ago, he got a surprise: a PhD student enrolled at a British university contacted him to say she wanted to jump ship.

Calster, a professor in Leuven University’s Institute of European Law, explains: “She had already started her PhD but was concerned her qualification might not be recognised in Europe after Brexit.” She was also worried because many PhD supervisors were leaving to go abroad, he says.

Many top European academics working in Britain arrived as young PhD students. Now universities fear discoveries and research are at risk because of a drop in applications from bright EU PhD candidates.

Early figures from the Russell Group universities reveal a 9% fall in non-British EU students starting postgraduate research courses in 2017-18, compared with last year – a big concern in universities that rely on European talent. Overall 16% of Russell Group PhD students are from the EU, but this rises to 27% for maths, 22% for computer science and 19% for the physical sciences.

Michael Arthur, president and provost of University College London, says: “If I look at the top research teams at UCL Europeans are over-represented, and many of them first came here as PhDs or post docs.”

Will the UK get a Brexit deal on research? That's the €160bn question | Ludovic Highman Read more

Arthur says he was relieved by the government’s December announcements offering “settled status” for Europeans already here, and the acknowledgement that his researchers can leave the country and work elsewhere for up to five years without losing that status. But many European researchers and students still fear for the future. “I try to reassure academics but it takes time to rebuild trust. There was a long period in which European citizens felt they were being used as bargaining chips. That has eroded confidence.”Calster can understand why young students are being put off Britain. “Just after the Brexit vote most of us assumed there would be some sort of coordinated, predictable approach. But that impression that things are under control and people will be reasonable is no longer valid.”

Other doubts contributing to the potential PhD brain drain include uncertainty over the right to remain after studying, and whether Britain will have access to EU research funds after 2020.

Jessica Cole, the Russell Group’s director of policy, says academics are still getting used to the idea of settled status.

Facebook Twitter Pinterest Geert van Calster of Leuven University, Belgium Photograph: Rob Stevens/Leuven University

“People doing a PhD here already now know they can stay. But the government needs to get that message out as forcefully as possible. Not only that you can stay – but that we want you to stay.”

Guillaume Charras, a French professor in biophysics at UCL, arrived from Paris to do his PhD. He went to Harvard and returned in 2007, becoming a big name in UK nanotechnology. As a research student he was attracted by how welcoming Britain was then.

“Part of the reason I decided to return to the UK was this openness. But now there is a very big question mark for people who are not yet in the UK and who haven’t already experienced that openness first hand.” Charras, whose lab has brought in £2m from the European Research Council in the past 10 years, says the biggest fear among all scientists is that Britain could be shut off from EU research cash.

The government has said Britain will remain part of the €70bn (£62bn) Horizon 2020 programme, which funds cutting-edge science, until its end. But official figures have revealed that Britain is already getting millions less from it – owing to a downturn in UK participation and success in winning grants. And many scientists are anxious about what will happen after 2021.

Brexit is hindering research collaboration, say EU universities Read more

“Some of the best scientists working in this country get European Research Council grants, and they are at the highest risk of leaving,” Charras says.

One of Glasgow University’s research stars, Tomasz Guzik, regius professor of physiology, agrees. “Brexit brings many unanswered concerns both about funding and about collaborations.”

Guzik, from Poland, is finding it harder to recruit European research students. “They all ask me ‘What will the future be like if I come?’ and I am not sure what to answer. But if we could give the clear message that Britain understands that science is a national treasure – then I am confident scientists worldwide will come.”

Many of his European colleagues are already leaving Britain. “I’ve received several approaches from Europe asking if I would be willing to move and bring this unique project and my team with me.”

Competitors outside Europe are spotting an opportunity. Andrew Timming, an associate professor at the University of Western Australia’s business school, recently advertised on Twitter for PhDs, urging them “jump from the sinking ship” of “Brexit Britain”. He says: “Does Brexit represent a recruitment opportunity? Absolutely. Not only do fewer potential PhD students want to study in UK universities, but there are also fewer opportunities for those who do.

Many PhD studentships are funded from European sources and this tap is now being turned off, with no firm commitment on the part of the British government to plug the funding gap,” he says.

John Dainton, professor of physics at Lancaster University and a spokesperson for the Campaign for the Defence of British Universities, says: “I feel like Britain is right back where we were in the 1970s when I was a young postdoc. We are losing young people.”

He spends a lot of time working in Europe, but says it is increasingly difficult to persuade talented young people he meets to relocate.

“If I tell someone they stand a good chance of getting a funded research fellowship at a UK university they will now still think twice because they see Brexit as a disconnect from opportunity.”

Brexit is striking right at the heart of science, he says.

“The very best science has always been international. It is about people in different places and fields pushing to get the best answers to big questions. National boundaries don’t come into that.”