The London School of Economics has reported that some of its academics have been banned from advising the Foreign Office on Brexit because they are not British.
The university said the leader of one of the projects has been told only UK passport-holders could be involved in talks on national security and foreign trade.
The Foreign Office has said nothing had changed following Brexit and that it would "continue to take advice from the best and brightest minds, regardless of nationality."
According to former Liberal Democrat leader Nick Clegg, who now acts as the party's EU spokesman: "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 policymaking."
The LSE has reported that after the referendum, a team of less than 10 researchers had been charged with providing policy advice to help ministers overcome any problems that might arise as the process of leaving the EU moves forward.
The LSE commented suggesting that its academics, including non-UK nationals, have a huge amount of expertise, which is vital during this time of uncertainty surrounding the UK's relationship with the EU.
A spokesman for the Foreign Office said: "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."
Deputy chief executive of Universities UK, Alistair Jarvis, said that foreign academics played an important role in providing advice and expertise to the government.