"We obviously regret the appearance of that but we don't see any way around it," Bret Walker SC told the court.

Mr Collaery has faced the ACT Court of Appeal on Monday in a high-profile appeal of the secrecy orders in his case but the public was forced to leave only a few minutes in.

The Canberra lawyer is fighting allegations he and his client the former spy Witness K conspired to reveal an unlawful Australian bugging operation ordered on the friendly foreign government of Timor-Leste while the two countries were negotiating a lucrative oil and gas treaty.

Monday's appeal is the latest in a long series of legal skirmishes that have dogged Mr Collaery's case.

From the beginning, then attorney-general Christian Porter used his powers under national security information laws to intervene in the case and have it heard behind closed doors.

The appeal follows a court ruling in the attorney-general's favour making orders that the case be heard in secret.

The government says these orders are necessary to protect Australia's national security.

Regardless of the outcome from this week, the question of the secrecy orders is almost certainly destined for the High Court.

Earlier, a procession of dark-suited lawyers had wheeled locked black trunks containing thousands of pages of documents into the courtroom.

Meanwhile, the Alliance Against Political Prosecutions held a rally outside attended by some 100 people and calling for an end to the prosecution of Mr Collaery and Witness K.

Human Rights Law Centre senior lawyer Kieran Pender said outside court that the prosecution of Mr Collaery and the secrecy around it, was wrong and undemocratic.

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"The NSI Act is broken and must be amended to better protect the public interest in transparency.

"The Attorney-General's use of secrecy in the Collaery case, to enable the Government to admit in Court that it spied on Timor-Leste, while refusing to admit that publicly, is undemocratic.

"The NSI Act makes a mockery of open justice, a vital democratic principle."

The appeal, before Chief Justice Helen Murrell, Justice John Burns and Justice Michael Wigney, is listed for two days.

Witness K, in separate proceedings in the ACT Magistrates Court, has indicated he will plead guilty and is next listed in June.

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