The documents show that a month into the job, Prime Minister Malcolm Turnbull wrote to retired judges Kevin Duggan and John Muir, appointing them as "public interest advocates". Although they are the only people able to argue against police requests for journalists' communications data in order to identify of a source, neither specialised in representing journalists or in media law.

The public interest advocate role was created under a last-minute amendment to the data retention legislation, meant to protect journalists and their sources from government access to their communications data.

Under the deal struck between the Coalition and the ALP, government agencies need a warrant before getting phone and internet data which would identify a journalist's source. But journalists are not notified that a warrant application has been made, and cannot argue against it. Instead, government-appointed public interest advocates are meant to make arguments about whether the public interest in the disclosure of the journalist's source outweighs the public interest in protecting source confidentiality.

Journalists face two years in jail if they reveal that a warrant has been sought. Justice Duggan is a criminal law specialist, who mostly presided over criminal trials during his 23 years on the South Australian Supreme Court. Justice Muir sat on the Queensland Supreme Court for 17 years.

Paul Murphy, the head of the journalists' union, the Media, Entertainment & Arts Alliance,  is disappointed with the appointments.

"The fact that the first appointments of advocates have been made and, as we always suspected, they have no background in media, in understanding the crucial importance of protecting journalists' sources in the public interest, just reinforces our view that this is a meaningless scheme," said Mr Murphy.

Former Media Watch presenter Jonathan Holmes describes the public interest advocate scheme as a "most extraordinary provision", because of its secrecy. "I don't have much faith that these judges will be powerful advocates, because the system does not allow them to consult with their so-called clients."

"It's purely window-dressing. I would be very surprised if there's ever a single instance where a public interest advocate is able to change the minds of whoever issues these warrants."

The Sydney Morning Herald approached the Prime Minister's office for comment and was referred to the Attorney-General. A spokesman for the Attorney-General said: "As former judges of the Supreme Court, Justice Duggan and Justice Muir are experienced in complex legal reasoning and well placed to consider and make submissions on competing public interest arguments.

"The appointments were made in line with the Public Interest Advocate regulations which require the advocate to be a Queen's Counsel or Senior Counsel or a former judge of a superior court."

When the laws were introduced, then-Communications Minister Turnbull described the public interest advocates as a "very important protection" for journalists. He assured them that there was nothing in the legislation that should concern journalists about their "right" to deal confidentially with sources. "All of us understand the work journalists do in a democracy is just as important as our work as legislators," Mr Turnbull said

The MEAA had argued for a fully contested warrant process, where media companies would be notified that government agencies were after their sources, and they could then oppose it. Under the laws, in force since October, phone and internet companies must hold on to their customers' communication data for two years. Twenty-one government agencies have access to metadata relating to phone calls, text messages, emails, downloads, and location information.

No warrant is required when agencies request the data of ordinary citizens. Each of the public interest advocates been appointed for a five-year term. Their appointments were not previously announced.