The law used to justify the raid on the home of Annika Smethurst is unconstitutional, the journalist’s lawyers have argued.

In submissions to the high court challenging the validity of the search warrant, Smethurt’s legal team said the offence breaches the implied freedom of political communication because it criminalises publications that are merely embarrassing to the government.

In April 2018, Smethurst reported that the heads of the defence and home affairs ministries had discussed draconian new powers to allow the Australian Signals Directorate to spy on Australian citizens for the first time.

The raid – along with a similar raid on the ABC headquarters for the Afghan files investigation – triggered a parliamentary inquiry into media freedom, while the ABC and Smethurst’s employer, Nationwide News, challenge the warrants in the courts to prevent possible prosecution of journalists and their sources.

The Smethurst warrant cited section 79(3) of the Crimes Act – communicating or allowing someone to have access to an official secret without authorisation – as the justification for the search.

In their submissions, Smethurst and Nationwide News lawyers accepted that the functioning of government “requires some information to be kept secret from the public”. But they argued the purpose of section 79(3) of the Crimes Act “is the protection of government secrecy as an end in itself, whenever that is thought desirable by the executive – and that purpose is illegitimate”.

They noted the offence extends beyond public servants, criminalising the conduct of people “unconnected with the commonwealth”, and contains nothing to limit the offence to “the kinds of information or circumstances that may justify secrecy”.

“The offence is committed whatever the document contains, whatever the motive for disclosure is and whether or not the disclosure is prejudicial to the state,” they said. “It applies whether the material in question is already in the public domain, wholly innocuous, or merely embarrassing to the government or its individual officers.”

The submission contrasted the old wording of the offence, which applied in April 2018 at the time of the raid, with the new provision, which came into force in December, and which required information to harm Australia’s interests or to be “inherently harmful”.

The submission also challenged section 79(1)(b), which it said created an “unconstrained discretion” to decide who had a duty not to communicate proscribed information, preventing publication by contractors, staffers or anyone without the minister’s permission.

It said the protection of secrecy of government information “as an end in itself, subject only to the will of the executive, is not compatible with the maintenance of the constitutionally prescribed system of representative and responsible government”.

“The entire basis of the implied freedom is that that system depends upon free communication about government and political matters.”

Smethurst and Nationwide News asked the court to rule the offence and the warrant were both invalid, and to order that police delete copies of electronic material taken from her phone.

A declaration of invalidity would “put an end” to the prospect that Smethurst could be prosecuted for the publication, the lawyers said.

In the wake of high-profile raids on Smethurst’s home and the ABC, police signalled they were investigating journalists for possible charges, not just their sources, a prospect they have never ruled out.

Attorney general Christian Porter has said he is “seriously disinclined” to approve prosecution of journalists and earlier in September issued a new directive requiring the Commonwealth Director of Public Prosecutions to seek his consent before prosecuting them for a range of secrecy offences.

The submission noted the pre-existing safeguard in section 85 of the Crimes Act requiring attorney general’s consent, but said the “unreviewable discretion” further compounded “the problem of executive control”.

In August the home affairs department head, Michael Pezzullo, told a joint parliamentary inquiry that the public servant who leaked a “top-secret” document to Smethurst “subject to judicial process and fair process … should go to jail”.

“It was designed to play into a Canberra game about which agency is asking other agencies to expand its powers or remits,” he said. “It is completely unacceptable for public servants to be playing in that way.”

The comments drew the ire of the Australian Law Council president, Arthur Moses, who described them as “emotive” and demonstrating the leak was “not relevant to national security” but rather “a game between two departments”.

In September police raided the Canberra home of intelligence officer Cameron Gill but have not confirmed whether the raid was related to the Smethurst leak.