One of the country's top universities has insisted it will stand by its foreign academics after it said the Government had banned them from advising ministers on Brexit because they are not UK nationals.
A bar on foreign experts at the London School of Economics (LSE) has been branded "utterly baffling" by former Lib Dems leader Nick Clegg.
LSE interim director Prof Julia Black said in an internal school update memo on the matter that the world-renowned university stood by its academic principles of independence.
"You may have seen reports in the media that the Foreign Office have advised us that they will be issuing tenders to contract for advisory work, but that only UK nationals will be eligible to apply.
"Whilst the Foreign Office has long had a rule restricting the nationality of employees or secondees, the extension of the bar to advisory work seems to be new.
"However, it is for the Foreign Office to determine what its national security arrangements are, and their legality, not for us.
"We are standing firm to our principles of academic independence and valuing our truly international community of scholars.
"We will continue to stand by our colleagues and we strongly value the work that you all do," she said in the memo, which was posted on Twitter by Jakub Krupa.
Sara Hagemann, an assistant professor at LSE's Europe Institute, said Government representatives told her they will no longer take advice from her or her non-UK colleagues.
A Foreign Office spokesman insisted nothing had changed since the pro-Brexit referendum result.
"The FCO regularly works with academic institutions to assist in its policy research, and nothing has changed as a result of the referendum.
"It has always been the case that anyone working in the FCO may require security clearance depending on the nature and duration of their work.
"Britain is an outward-looking nation and we will continue to take advice from the best and brightest minds, regardless of nationality."
Mr Clegg, now the Lib Dems European Union spokesman, said: "It is utterly baffling the Government is turning down expert, independent advice on Brexit simply because someone is from another country.
"This is yet more evidence of the Conservatives alarming embrace of petty chauvinism over rational policy making."
Steve Peers, a professor of EU law at the University of Essex, said: "What kind of know-nothing nativist Government rejects the expertise of all non-citizens?"
The move is reportedly due to concerns over sensitive data being exposed during Brexit negotiations.
Ms Hagemann tweeted: "UK govt previously sought work & advice from best experts. Just told I & many colleagues no longer qualify as not UKcitizens #Brexit"
A spokesman for LSE said: "The UK Government regularly calls upon LSE's world-class academics for their advice on a range of issues.
"We believe our academics, including non-UK nationals, have hugely valuable expertise, which will be vital in this time of uncertainty around the UK's relationship with Europe and the rest of the world.
"Any changes to security measures are a matter for the UK Government."
It comes just days after Home Secretary Amber Rudd outlined proposals to make British firms publish lists of their foreign workers, a move which has prompted criticism from businesses and her own brother.
SDLP MP for South Belfast, Alasdair McDonnell MP, strongly criticised the government’s decision. Dr McDonnell said: "Many of us were deeply disturbed by the xenophobic and anti-immigrant rhetoric witnessed at the Conservative Party Conference this week. Perhaps then it should not be surprising that the government is leading by example on its policy of ‘British jobs for British people’.
"There is a suggestion that the Foreign Office has introduced this policy in order to avoid sensitive material relating to Article 50 negotiations being leaked.
"These security concerns ring hollow. This almost Cold War like suspicion of foreign nationals not only risks jeopardising our negotiations with the European Union: it is deeply insulting to the professionalism and integrity of these academics and reeks of xenophobia.
"Up until a few days ago, these academics were considered key experts in EU affairs and policy by the Foreign Office. It now appears that the Foreign Office no longer requires their expertise solely on the basis of their nationality.
"It seems that the government’s full embrace of populist anti-immigration policies takes precedent over the need for the best expertise possible as we navigate the unchartered waters of leaving the European Union."