Tony Abbott has described Dyson Heydon as “absolutely beyond reproach”. Which is exactly the problem.

“This government will certainly defend the integrity of the royal commissioner,” the prime minister said after it was revealed Heydon had been forced to pull out of a fundraiser for the New South Wales Liberal Party.

“This royal commission is necessary because of the rorts, rackets and rip-offs which have been exposed inside the union movement. If members opposite were more interested in looking after workers and less interested in looking after themselves, they would support this royal commission.”

The attorney-general, George Brandis, dismissed any suggestion of political bias as “disgraceful” and “absurd”. As is the preference of this government, he seems to believe that any misdemeanour can be corrected after the fact and once repaired should never again be mentioned.

“My understanding is that Mr Heydon has decided not to speak at the event and I frankly think that should be the end of it,” Brandis said. “There is no more eminent lawyer in this country than Dyson Heydon… He is a person of complete and punctilious personal integrity.”

Unfortunately for Heydon, the question is not one of eminence but judgement.

It is possible he did not realise the Sir Garfield Barwick Address was a party fundraiser. A shortage of stationery might have put its invitations on NSW Liberal Party letterhead. The famous culture of disclosure in political fundraising might have caused the conscientious inclusion of a note saying, “All proceeds from this event will be applied to state election campaigning.”

On Thursday, Heydon’s office issued a statement dealing with the matter: “As early as 9.23 this morning – and prior to any media inquiry being received – he advised the organisers that ‘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’.”

Heydon is almost unrecognisable in the release, not least in describing 9.23am as early. This is a man who boastfully rose at 3.30 each day so that he might be at chambers by 10 past five.

But this scandal is interesting not because of what it says about Heydon but what it says about the royal commission he is chairing. Heydon, we already know. He is the black-letter conservative spirited onto the High Court by John Howard after a persuasive speech at a function for Quadrant. He is the dissenter who would see no problem with indefinite detention, who had no real concerns about the legality of the Malaysia Solution or the various state bikie laws or the funding of school chaplains, who was against fiscal stimulus during the global financial crisis and who would have barred legislation for the plain packaging of cigarettes.

Heydon has been critical of union finances since as far back as 1989, when he co-authored a report on them for the Greiner government in NSW. It should be no surprise that he would address a Liberal Party function, but to his opponents it makes worse the appearance that he is also chairing one – a $60 million witch-hunt; a commission established to embarrass a former prime minister, that in failing to do so had to ask for a one-year extension to go find something else.

The union movement is flawed. All movements are. But from the start, the commission established to investigate it has been more flawed still. It may yet damage unionism, but the greater shame is the damage it does to this country’s key system of independent inquiry. The black-letter lawyer should surely see this.