High Court hears appeal on NSW parliamentary witness arrest powers

A showdown between the New South Wales premier's top staffer and the upper house has played out in the High Court over whether he can be arrested and hauled before a parliamentary inquiry.

Powers dating back to the 19th century were declared non-existent by the NSW Court of Appeal last December after Chris Minns's chief of staff, James Cullen, launched a legal challenge.

Mr Cullen faced being detained and forced to give evidence before a committee after he refused to attend its inquiry into the leaking of confidential minutes.

Others have since used the ruling to dodge questioning by the state's elected representatives.

An appeal by Legislative Council president Ben Franklin was heard on Thursday before Chief Justice Stephen Gageler, and Justices Michelle Gordon, James Edelman, Jacqueline Gleeson and Robert Beech-Jones.

A phalanx of 14 barristers spread across the bar table in Canberra, with the Commonwealth, South Australia and Northern Territory intervening in the case and Liberal MLC Damien Tudehope appearing as a non-party helping the court.

The case is about the validity of sections 7 to 9 of the Parliamentary Evidence Act 1901, which provide a process for the arrest of a witness who fails to turn up and give evidence when summoned.

The president may "certify" the witness's non-attendance to a Supreme Court judge, who then "shall" issue an arrest warrant to bring the person before a chamber or committee to give evidence.

It is the role of the judge that the Court of Appeal deemed the "constitutional vice" of the scheme because it made the judge a "mere functionary" with "no choice but to sign and seal the warrant".

It was decided this substantially impaired the "institutional integrity" required of state courts under the Australian Constitution as it gave an "appearance of judicial authority" to a decision already made "in substance" by the president.

Taxpayers set to foot huge legal bill

The president's legal team, led by Bret Walker, SC, argued the Court of Appeal's conclusion was "inconsistent with the history of the constitution and the assumptions on which it was framed".

In written submissions, Mr Walker pointed to the fact the warrant power in the 1901 Act was first conferred upon the Supreme Court 20 years earlier in the Parliamentary Evidence Act 1881.

"That suggests that, at the time of Federation, the function was not thought to be incompatible with the independence and impartiality of the Supreme Court," Mr Walker wrote.

"The Constitution assumes that, at Federation, the Supreme Courts were independent and impartial tribunals."

According to an outline of his oral argument, Mr Walker said if a judge could scrutinise the basis for an arrest warrant, it would be inconsistent with a Bill of Rights prohibition on courts interfering with proceedings in parliament.

Brendan Lim, SC, for Mr Cullen, said this principle was "a shield, not a sword", according to a summary of his oral argument.

"[It] can explain why a court does not interfere with the intra-mural affairs of Parliament but not why a court may be required to lend its authority to such an intra-mural affair," Mr Lim said.

Whoever wins, taxpayers are set to foot a huge legal bill.

At budget estimates in August, Clerk of the Parliaments and Clerk of the Legislative Council Steven Reynolds revealed the original action cost $443,518 to defend.

The High Court appeal, Mr Reynolds said, cost $384,620 as of July.

He added the president was ordered to pay costs of about $250,000 to Mr Cullen, whose fees are being covered by a government grant.

NSW Opposition Leader Kellie Sloane said on Thursday it was "absolutely appalling".

"It is an outrageous undermining of our democracy in NSW."

Mr Cullen declined to comment.

Public paying more than legal bill

The public is paying another price: its capacity to interrogate government activity and other matters of public importance, through its elected representatives, is diminished.

As Mr Reynolds told estimates, three key witnesses declined to appear at an inquiry into identity protections, citing the Cullen ruling, and numerous others refused to front a committee probing data centres.

"Witnesses now, it's widely known that they can't be compelled to attend," Mr Reynold said.

Mr Franklin told estimates the issue caused him significant concern.

"The problem with this broadly is that the people who we particularly need to appear and want to appear, I suspect, are the ones going to be most likely to avail themselves of the opportunity not to appear," Mr Franklin said.

The Coalition has introduced legislation to restore the powers to force witnesses to front inquiries, but the government has refused to consider it pending the High Court appeal.