While Mr Dreyfus did not specifically request a federal police probe, he said the "damaging leak" risked undermining Australia's national security and asked Mr Turnbull to order an investigation. "I am sure I do not need to emphasise with you the gravity of such a security breach," Mr Dreyfus wrote. "The documents described in the media appear to be extremely sensitive and divulge information about one of Australia’s key security agencies. "It is therefore incumbent on you to establish an investigation into how such sensitive information held by members of your government was able to find its way into the public domain. "Ensuring this sort of breach cannot occur again is vital for securing the trust that Australians place in governments on matters of national security."

Mr Dreyfus has since argued that Smethurst's reporting was in the national interest, as has Labor leader Anthony Albanese. Loading "I think it is a good thing that that was reported, frankly," Mr Albanese said this week. "Australians do have a right to know what is going on in a democracy." While Mr Dreyfus argued in his letter that the leak was a national security matter, he this week said Smethurst's April 2018 report did not threaten national security. On Thursday, he told ABC radio: "What is it about Australia’s national security – this is the question the government has to answer – what is it about Australia’s national security that is so threatened by a public discussion of a proposal to allow the Australian Signals Directorate for the first time to spy on Australians?"

In a separate interview on the same day, he said: "I don’t accept that there is some national security reason there for not discussing it." If found and convicted, the source of the leak faces a jail sentence of up to two years. In a statement on Saturday, Mr Dreyfus said: "I have never disputed that this leak was of a very serious nature, nor that it should have been looked into. My concern has entirely centred around the raiding of a journalists’ home and the government’s abdication of its responsibility to uphold the principle of press freedom. "My concern at the time was that the internal chaos of the Turnbull government could compromise the proper functioning of government, as expressed in the letter." Mr Dreyfus' letter suggested tensions inside the government over Peter Dutton's newly created Home Affairs super portfolio may have been behind the leak to Smethurst.

"The chaos inside government cannot be allowed to interfere with the vital work of our security agencies, or indeed any other arm of the public service engaged with national security," Mr Dreyfus wrote. "As the government of the day you are the custodian of our nation’s safety. At present your ability to carry out that duty is in question." In a meeting of the national security committee of cabinet in the days after Smethurt's story, Mr Turnbull swiftly put to bed any thoughts of using the international spy agency to monitor Australians. Government officials have long been adamant there was never a plan to spy on Australians. Rather, the potential expansion of the ASD's role involved using the agency's capabilities to disrupt in the systems of cyber-enabled criminals such as paedophile rings and organised crime gangs in Australia.

But the change would nonetheless have meant the ASD was carrying out domestic activities in ways it had not been previously. Home Affairs secretary Michael Pezzullo has previously said that department heads "are obliged" to refer unauthorised disclosures of classified advice to the police investigation. Shadow attorney-general Mark Dreyfus at Parliament House in Canberra. Credit:Fairfax The AFP is also examining the disclosure of highly classified material to the ABC, which it raided this week in addition to Smethurst's home. The ABC's stories used leaked Defence information to accuse Australia's elite special forces in Afghanistan of killing unarmed men and children. While the AFP is investigating the leaks to Smethurst and the ABC, is has abandoned any inquiry into who leaked classified national security advice at the height of a major political dispute over border protection.