A landmark High Court case set to determine states’ rights is on the brink of collapse, after one defendant, the South Australian government, turned on the other, the state-appointed Murray–Darling Basin royal commissioner.

The SA government is refusing to grant an extension of the commission’s February 1 reporting deadline or offer any extra funding, despite the possibility a victory in the High Court case could provide the commission with extra witnesses and new evidence to examine, just before the end of the year.

That lack of a state government guarantee means the commissioner, Bret Walker, SC, will now likely have to withdraw a series of summonses for federal government documents and for current and former Commonwealth officials to give evidence.

The Turnbull government is refusing to accede to the summonses. Instead, it launched the High Court action, challenging the state-based royal commission’s power – as set out in the South Australian Royal Commissions Act – to compel Commonwealth agencies.

All states except Victoria have joined the case, which will have far-reaching implications for the enforceability of other agreements between states and with the Commonwealth if it proceeds.

The federal and SA governments are now being accused of working together to nobble the commission, which is examining how the Murray–Darling Basin plan was drafted and implemented. Whether any laws have been – or are being – broken is central.

It is fairly standard for royal commissions to seek an extension.

It is equally standard for governments, if asked, to grant them.

That this royal commission is established under state, not federal, law is key to why these conflicts have arisen.

“The commissioner is being squeezed from both sides. It’s like the state and federal governments are colluding.”

SA Centre Alliance senator Rex Patrick, whose party was formerly the Nick Xenophon Team, has condemned the refusal to assist.

“The commissioner is being squeezed from both sides,” Patrick told The Saturday Paper this week. “It’s like the state and federal governments are colluding.”

Patrick won support from Labor and the Greens on Wednesday to have the Senate issue its own demand for the documents. Unlike the state-based royal commission, the Commonwealth parliament’s power to make such an order is not in dispute.

If the information is provided only through that process, it will be covered by parliamentary privilege and may not be able to be tendered as evidence in that form to the royal commission, although other witnesses could potentially draw on its contents in their own evidence.

But Patrick argues providing the requested evidence to the Senate would underline the absurdity of the government’s refusal to give it to Bret Walker. He is also putting pressure on the government to abandon its objection and volunteer the witnesses to the commission, by using the implied threat of withholding his vote on future legislation in the Senate that the government will need his support to pass.

“This decision to fetter the commissioner on purely legal grounds in circumstances where they say they have nothing to hide is conflicted and unsupportable,” Patrick says. “It’s also not in accordance with the openness and transparency expected of responsible government and has caused us a loss of confidence in the federal government and that is one of the foundations upon which good-faith negotiations are conducted.”

He warned that his colleagues in the SA upper house, MLCs Connie Bonaros and Frank Pangallo, were inclined the same way “in retaliation” for the state government’s refusal to extend the commission’s reporting time.

The royal commission was established under the former SA Labor government, which lost office in March this year. Its work appears now to be falling victim to politics.

The new Liberal SA government let the commission continue as it had promised during the election campaign, but relations have become increasingly tense, with information about the commissioner’s salary – $10,000 per hearing day – leaked to Adelaide’s main newspaper, The Advertiser.

The deteriorating relationship reached a flashpoint on Thursday of last week, when commissioner Bret Walker wrote to the South Australian attorney-general Vickie Chapman.

It was a long and complex legal letter with a question at its core: was Chapman willing to extend the royal commission’s reporting deadline beyond February next year, if necessary?

While he couldn’t be certain yet, Walker laid out why he was seeking an early indication about an extension, explaining the timing of the High Court proceedings could make the existing deadline impossible to meet.

The court might reject his authority to issue the summonses, in which case they would be withdrawn, or it might uphold his authority, meaning the evidence would become available and would put pressure on the deadline.

But it is the third, catch-22 scenario that required an early indication from the state government. Boiled down, it is that while the High Court’s judgement would determine the need for an extension of time, the prospective grant – or refusal – of an extension would also determine if there was a High Court case at all.

That’s because the High Court can only hear matters in which its decision will have a practical impact, resolving a real dispute. It cannot hear cases based on a matter of principle alone, such as whether states can force the Commonwealth to do something. The lack of a practical impact renders a case hypothetical and unable to be heard.

In this case, the commissioner’s available time to consider new evidence would be bookended by the High Court hearing, set down for two days in late October, and his February reporting deadline.

Walker indicated that even if he and the SA government – joint defendants – won the case, there would not be enough time to afford the witnesses procedural fairness, something required by law.

Procedural fairness would include giving them time to prepare statements, obtain legal counsel if necessary and give evidence – unlikely before mid November at the earliest. Only then could the commissioner consider that evidence alongside all other evidence, call other witnesses whose testimony might be required as a result, write his report and allow anyone against whom there may be adverse findings to respond before publication. Walker argued it would be impossible to guarantee all of these steps could be completed before the February deadline, telling Chapman that unless an extension was definitely obtainable, he was obliged legally to say he was unable to receive and hear the new evidence, even if the High Court decision made it available.

That would see the case collapse before it began, rendering it hypothetical. The court would refuse to hear it at all – a lose-lose situation in terms of gaining access to the witnesses and documents.

Walker said in his letter that unless the possibility of an extension of time could be indicated now, this inability to use the evidence would force him to withdraw his summonses.

While the above is a short summary of the commissioner’s letter, the attorney-general’s reply was considerably shorter and landed in a different place entirely.

Chapman replied to Bret Walker in a letter dated that same day, August 9. “Dear commissioner,” she wrote. “I understand from your letter that you consider that you are able to complete your report without the benefit of the materials and evidence sought in the summonses in question. I note that you have not requested any extension of time within which to provide your report.”

Chapman said she also noted Walker was obliged to withdraw the summonses “and that this will have the likely consequence of rendering the proceedings moot in the view of the High Court”.

She thanked him for drawing this to her attention and looked forward to receiving his report “in due course”.

There is no mistaking Walker’s mood in the wording of his August 10 reply.

“Dear Attorney,” he wrote, thanking her for the response he said pointedly he had just received, despite it being dated the previous day. “I am afraid there has been some misunderstanding. It should be cleared up as soon as possible.”

He corrected the attorney-general’s interpretation, and said it was “unthinkable” that either he or the state government would proceed through a High Court case “on a feigned basis – with me standing so as to allow the court to proceed as if their decision in our favour were to have utility, if that were not true”.

The last five words were underlined.

Walker told the attorney-general her reply did not engage with his request “at all” and that he “respectfully and urgently” sought an answer on whether an extension would be granted if needed.

He said it would be her answer – yes or no – that determined whether he withdrew the summonses or not.

As his letter reached its conclusion, Walker indicated that while he had been writing, he had discovered Chapman had issued a press release that morning, announcing Walker intended to withdraw the summonses. His tone bristled. “It is wrong, discourteous and inappropriate,” Walker said of the statement, which purported to speak on behalf of an independent royal commissioner.

He noted it was particularly wrong to blame him for any decision to withdraw the summonses, as that would only arise from a decision by her government that rendered him unable to enforce them.

“The media release should be completely withdrawn,” he wrote. “I am owed an apology.”

There was no such mea culpa in Vickie Chapman’s next letter, which also confirmed her position on an extension. The answer was no. “Dear Mr Walker,” she wrote, noting his comments in response to her media release. “I can confirm that the South Australian Government intends to maintain the existing time frame for the Murray–Darling Basin Royal Commission, as established by the former state government. I also note that the Government is providing funding of $8.5 million for the Commission. We do not intend to provide further funding.”

Chapman thanked him for his work and looked forward to his report “in February 2019”. And that was that.

At time of press, Walker had not yet withdrawn his summonses. It appeared, though, that was the next step.

Meanwhile, Rex Patrick was continuing his campaign in Canberra for more transparency around the Murray–Darling Basin Plan.

“Basin communities have a need – indeed a right – to be able to study and understand all that sits behind the plan,” Patrick told the senate on Wednesday. “… We have now got a royal commissioner who is snookered between a federal government’s refusal to assist and the state government’s refusal to grant extra time. It’s essential to building and maintaining confidence in the plan … What is the federal government afraid of? What is the federal government trying to hide here?”

These are just some of the many questions to which answers are not yet forthcoming.