An Australian lawyer acting on behalf of WikiLeaks founder Julian Assange is due to arrive in Sydney this morning amid claims she was initially barred from boarding the flight.

Jennifer Robinson, who has represented Mr Assange in his British legal challenge against extradition to Sweden, says she was stopped at London's Heathrow airport on Thursday and told she could not board a plane to Australia until she was cleared by the Australian High Commission there.

Using Twitter, she said: "Just delayed from checking in at LHR [London Heathrow Airport] because I'm apparently 'inhibited' - requiring approval from Australia House... to travel."

She wrote that an immigration security guard said to her: "You must have done something controversial because we have to phone the embassy."

Ms Robinson continued to say she had been put on a "certain government agency's" list.

She then tweeted directly to the Department of Foreign Affairs and Trade, asking: "Please explain: What is the 'inhibited' travel list? And why am I now apparently on it?"

Ms Robinson is due to speak at a legal conference today.

Her supporters in the legal fraternity, including Australian Lawyers Alliance president Greg Barns, have been angered by the incident.

"Jennifer Robinson is a lawyer who is acting for Julian Assange, and she should be able to travel anywhere she likes in the world," Mr Barns said.

"There should be no valid reason why this should happen and the Australian government needs to provide an explanation," he said.

"Right through this issue it has obfuscated, refused to provide assistance to Mr Assange, and now the Australian government, working with the UK, has put his lawyer on an inhibited persons list."

'Extraordinary'

Mr Barns said he had never heard of such a list.

"This is just extraordinary that a lawyer, acting for a client would be placed on such a list and the Australian government - if it doesn't have anything to do with it, needs to get an explanation from the UK government and that explanation needs to be made public," Mr Barns said.

Attorney-General Nicola Roxon has repeatedly told the media that Australian consular officials have afforded Mr Assange the same consular assistance any citizen in his situation would enjoy.

A DFAT spokesman said the department was not aware of any restrictions applying to Ms Robinson's travel.

"As an Australian with a valid passport, she would be free to return to Australia at any stage," the spokesman said.

"The UK border authorities or airline of travel may be able to provide further insight on claims that she was impeded from boarding her flight."

Speculation

The ABC has asked the department a series of questions regarding Ms Robinson's claims and the level of its cooperation with British immigration officials.

Questions have also been posed to the British government.

There has, in addition, been speculation in legal circles that Ms Robinson's involvement with the case of Bradley Manning in the United States - the soldier alleged to have leaked secret US cables to Wikileaks - or her involvement with human rights cases in Indonesia's Papua provinces, may have been factors in the Heathrow incident.

The term inhibited appears to be used US security agencies.

According to a US department of homeland security document, dated October 28, 2008 and uncovered by Crikey journalist Bernard Keane, "inhibited status" is a US security term.

The document says: ''Inhibited status... means the status of a passenger or non-travelling individual to whom TSA [Transport Security Administration] has instructed a covered aircraft operator or a covered airport operator not to issue a boarding pass or to provide access to the sterile area."