Mr Collaery, a Canberra lawyer and former politician, is awaiting trial in the ACT Supreme Court on charges of unlawfully communicating information about the Australian Secret Intelligence Service and conspiring to do so.

The allegations relate to the spying agency's bugging of the East Timor government in 2004, when the impoverished country was negotiating with Australia over lucrative oil and gas reserves.

Mr Collaery's trial was set to be shrouded largely in secrecy until the ACT Court of Appeal ruled in October that it should be mostly open.

Three judges of that court said, in a one-page judgment summary, that they doubted a significant risk of prejudice to national security would materialise if certain things the Attorney-General wanted to keep hidden were in fact disclosed to the public during the trial.

Chief Justice Helen Murrell, Justice John Burns and Justice Michael Wigney added that secrecy risked damaging public confidence in the courts, while open justice deterred "political prosecutions".

Chief Justice Murrell was due to publish the court's full judgment, albeit with some redactions, in November.

But she ended up being unable to because Tim Begbie QC, a barrister for Attorney-General Michaelia Cash, flagged the possibility she would appeal to the High Court and argue the judgment should not be released without greater redactions.

An application for special leave to appeal was filed in that court last Friday, which was the final day it could possibly have been done.

The document, since obtained by Human Rights Law Centre senior lawyer Kieran Pender, has been provided to The Canberra Times.

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Three lawyers for Senator Cash, including Mr Begbie and Solicitor-General Stephen Donaghue QC, argue in the application that information "likely to prejudice national security will be made public" unless the appeal is upheld and publication restricted.

They say open justice is of "undoubted importance", but national security considerations must be given "the greatest weight".

"Sometimes, as in this case, an appeal is the only way to prevent prejudice to national security," the application concludes.

It is not yet known when, if at all, the High Court will hear the special leave application.

Mr Collaery's case was, meanwhile, back briefly before the Supreme Court on Wednesday, when the next lot of proceedings were listed for February 7.

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