A lawyer for WikiLeaks founder Julian Assange claims she was stopped at Heathrow Airport and told she was on a watch list requiring official approval before she could return to her native Australia.
Jennifer Robinson said a member of airport security told her she "must have done something controversial" and that they would have to contact the Australian High Commission in London before letting her on her flight.
The Australian human rights lawyer was later allowed onto a plane bound for Sydney, where she is due to speak at the Commonwealth Law Conference tomorrow.
Australia's Department of Foreign Affairs said it was "not aware" of any restrictions on Ms Robinson's travel and added that its High Commission in London had no record of receiving a call from the British authorities about her movements.
Ms Robinson wrote on Twitter at 9.30pm last night: "Just delayed from checking in at LHR (London Heathrow) because I'm apparently 'inhibited' - requiring approval from Australia House dfat (the Department of Foreign Affairs) to travel...
"Security guard: 'you must have done something controversial' because we have to phone the embassy. 'Certain government agencies' list."
She met Assange - who is fighting extradition to Sweden to face sex crime allegations - on Monday, according to a Tweet from the official WikiLeaks account.
The Commonwealth Lawyers Association (CLA), which is organising the conference at which Ms Robinson will appear, voiced concerns about the incident.
It said in a statement: "If these reports are accurate, then the CLA believe they raise profound issues concerning the independence of lawyers and their clients.
"The CLA points out that Article 13 of the UN Principles on the Role of Lawyers sets out clearly that 'lawyers shall not be identified with their clients or their clients' causes as a result of discharging their functions'."
An Australian Department of Foreign Affairs spokesman said: "We are aware of claims by Jennifer Robinson, a member of Julian Assange's legal team, that she was prevented by UK border authorities from boarding a flight in London because her travel was in some way 'inhibited', and that she would not be able to travel without prior approval from Australian officials.
"As the Department of Immigration and Citizenship confirmed publicly earlier today, no Australian government agency prevented Ms Robinson from boarding her flight at London's Heathrow Airport.
"We are not aware of any Australian government restrictions applying to Ms Robinson's travel.
"As an Australian with a valid passport, Ms Robinson would be free to return to Australia at any stage.
"The Australian High Commission in London has no record of a call being received from UK authorities concerning her travel.
"We understand Ms Robinson has today departed London on a flight to Australia.
"We are seeking to verify Ms Robinson's claims with relevant UK authorities."
Assange, an Australian former computer hacker, made headlines around the world with revelations from secret US military files and diplomatic cables released by his controversial whistle-blowing website WikiLeaks.
He is awaiting the outcome of his appeal to the Supreme Court, the highest court in the land, against being extradited to Sweden.