A lawyer for WikiLeaks founder Julian Assange was stopped at Heathrow and told she was on a secret watch-list and required special clearance before she could board her plane, the Daily Mail reported.
Australian national Jennifer Robinson said she was stunned after being told by an airline crew member that she was on an "inhibited person list" that meant she must have "done something controversial".
In April, she booked a Virgin Atlantic ticket from Heathrow to Sydney, where she was to attend a Commonwealth lawyers' conference. Eventually, she was issued a boarding pass and allowed to catch her flight.
Robinson said she could not understand why she was on the list as she had never done anything controversial or criminal.
She said that under Australian law, a citizen does not need special clearance when returning to their own country, regardless of whether they are on any watch-lists.
According to the Daily Mail, although WikiLeaks supporters believe the list may be a secret US or British watch-list that monitors international movements of certain individuals, both governments have denied they have such a database.
The Australian government has also denied having such a list.
The 31-year-old human rights lawyer is a member of Assange's legal team that has been fighting his extradition to Sweden on alleged sexual assault offences.
She was also his legal adviser when WikiLeaks published US military documents as well as diplomatic cables from American embassies.
Virgin Atlantic did not comment on the case, the report said.