The hearing before Justice Michael Wheelahan comes as research conducted by progressive think tank The Australia Institute reveals three in 10 FOI decisions are late and one in two are successfully challenged. There are 957 reviews before the Australian Information Commissioner that are over 12 months old, and 60 reviews that are four or more years old.

Mr Hardiman, Australia's first Freedom of Information Commissioner in seven years, resigned earlier in March citing a lack of power to reform the backlogged system he was hired to fix.

"We currently have an FOI regime that is broken," Mr Patrick told The Canberra Times. "Delay is the enemy of FOI and the Information Commissioner is aiding and abetting that enemy."

The Australian Information Commissioner said it seeks to complete its requests as "efficiently as possible" but was limited by resourcing constraints.

The self-described "transparency warrior" said he is using the case against the Information Commissioner - which has cost the agency somewhere between $700,000 and $1 million - as a "heavy leverage point" to pressure the Albanese government to properly resource the office dealing with contested freedom of information cases.

The former independent senator also cites an affidavit from the Attorney-General Mark Dreyfus, deposed in opposition and seen by this masthead, saying FOI delays have hindered him doing his job as a federal member of Parliament scrutinising government activities.

"I think the court will rule that FOI must be dealt with in a reasonable time frame. It's up to Mark Dreyfus to properly resource the office," he said.

"If you look at Mr Hardiman's resignation posted on LinkedIn, you will see he talks about his inability moving forward to meet the objectives of the Act and he then says that the necessary remedies are outside of his power.

"I don't think he was talking about any legislative power. I think he was talking about the power to properly fund FOI in Australia."

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The former senate crossbencher is seeking a judicial declaration as to what is a "reasonable" time frame for an Information Commissioner to answer a request for a review on a FOI decision, as there is no statutory time frame to make a decision.

An Information Commissioner spokesperson said review applications had risen by around 63 per cent last year alone due to a number of factors.

"A significant legacy caseload and an increasing number of IC reviews, combined with the impact of the COVID-19 pandemic, have affected our ability to deal with this caseload, given the resources we have available," the spokesperson said.

"Notwithstanding these challenges, the OAIC has significantly increased the number of IC reviews we finalise each year and we continue to seek to improve the timeliness of IC review processing."

Mr Patrick has more than 20 contested FOI applications awaiting a decision by the Information Commissioner, some from more than three years ago when he was in Federal Parliament. They relate to Greater Sunrise oil and gas resources, Foreign Investment Review Board decisions, COVID-19 border closures, Snowy 2.0 details and stage three tax cuts.

"I have just filed a final affidavit which includes Mr Hardiman's departing statements, I think they are highly relevant to the matter and will bring considerable weight to the argument that is before Justice Wheelahan," he said.

"Most FOI reviews are taking more than three years to process. In that time, contemporary issues become historical issues and governments to which there ought to be scrutiny applied are no longer in government."

But ultimately, Mr Patrick wants better resourcing for the office of the Information Commissioner.

"This becomes a heavy leverage point to put pressure on the government," he said.

"In some sense, I've had the Attorney-General intervene in my favour. Yet, we're actually seeing more than what I think will amount to a million dollars of taxpayers money being spent resisting my view that FOI matters should be dealt with in a short time frame."

Mr Patrick has lawyers working on the case, pro bono, and has been indemnified by the Grata Fund and the Australia Institute in the event he is unsuccessful.

The Canberra Times has contacted the offices of the Attorney-General and the Australian Information Commissioner for comment.

The Federal Court decision is expected later this year.