Labor is demanding the resignation of the head of the royal commission into union corruption following revelations he agreed to speak at a Liberal Party fundraising event.

Commissioner and former High Court judge Dyson Heydon was advertised as the guest speaker at the $80-a-head Sir Garfield Barwick address in Sydney later this month.

The event was organised by the legal branch of the New South Wales Liberal Party and first advertised in April.

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The politically-branded invitation promoted Justice Dyson’s appearance and offered guests the option to make cheques “payable to the Liberal Party”, saying proceeds would be “applied to state election campaigning”.

Revelations that the person appointed by the Prime Minister to investigate unions would speak at a Liberal Party event triggered a ferocious reaction from the ALP.

During question time, the manager of opposition business Tony Burke said the commissioner had revealed deep bias and partisan links.

“He is conflicted, he is biased, the royal commission is a farce. Dyson Heydon is in a position now where he cannot remain in that role,” Mr Burke said.

“The sham – that we have said for so long this royal commission was – has now been found out and exposed.”

Manager of Opposition Business Tony Burke said the commissioner had revealed deep bias. Photo: AAP

The feverish response to the news is in sharp contrast to the man himself.

During a hearing this week, Justice Heydon intervened when one lawyer demanded to know why a witness was taking a “long pause” before answering a question.

Justice Heydon begged to differ, saying the pause was only for four seconds.

After leaving the High Court, Justice Heydon explained to the ABC that he did not write judgments with his fellow judges because he was a stickler for proper English who abhorred split infinitives and dangling participles.

“Well they don’t write grammatically as I understand Anglo-Australian grammar,” he said.

Yet Justice Heydon, who was a professor of law at age 30, failed to detect that the invitation to the lawyers and judges – which was first advertised in April – said that funds would go to the NSW Liberal Party.

He released an email sent at 9.23am on Thursday by his assistant to event organisers:

“If there was any possibility that the event could be described as a Liberal Party event he will be unable to give the address, at least whilst he is in the position of Royal Commissioner.”

Fairfax Media says it first contacted the commissioner’s office about the guest-speaking story at 9.35am, before publishing a story which dominated question time in the federal parliament and beyond.

Invitation to the Liberal Party Fundraiser involving Dyson Heydon.

Labor and the unions are not buying that explanation, saying the row proves what they’ve been saying all along – that the royal commission is a political witch-hunt established by the Abbott government to target its enemies.

During the hearings, Justice Heydon has repeatedly noted that royal commissions, unlike courts, are not bound by the rules of evidence. But royal commissions are a powerful institution and they, too, have to be seen to be doing the right thing.

As the High Court has noted in one judgment, delivered during Justice Heydon’s time on the bench, it is fundamental to the administration of justice for a judge to be neutral.

“It is for this reason that the appearance of departure from neutrality is a ground of disqualification,” the judgment said.

“Because the rule is concerned with the appearance of bias, and not the actuality, it is the perception of the hypothetical observer that provides the yardstick. It is the public’s perception of neutrality with which the rule is concerned.”

All royal commissions are “political” in being appointed by and reporting to the government of the day, which agrees to their terms of reference and to their main players, such as the commissioner and counsel assisting.

But the Abbott government seems to see transparency as a one-way mirror, refusing to answer many questions itself but establishing inquiries that have hauled in the last three Labor leaders – Kevin Rudd, Julia Gillard and Bill Shorten.

The government says the Heydon royal commission was needed to expose systemic misbehaviour and poor governance within the Australian union movement, as shown in the case of the Health Services Union.

As things stand, the government has strongly backed Justice Heydon to stay at the commission, which is due to report by the end of the year.

Rumours have swirled in recent weeks that the government was considering extending the inquiry into 2016 when the Federal election is expected. The events of this week make that less likely.

Mark Skulley is a freelance journalist who is based in Melbourne. View all of his columns here.