Leung told reporters in the morning that he had made revisions to a document Chow presented to the committee, asking for a “complete and comprehensive probe”.

“I am a subject of investigation, and I have the complete right to express my views to Legco of the investigation’s scope,” Leung said as he also urged an investigation into the leak of the confidential document revealing his input.

Chow, who is also a solicitor, apologised for his “lack of political sensitivity” in not informing the committee of the chief executive’s personal input, but he insisted there was nothing wrong in discussing the matter with Leung in private, just as “a prosecutor would liaise with a defence lawyer on agreed facts before a trial”.

That added fuel to the fire, with pan-democrats reminding Chow that he should be a neutral party on the committee instead of working secretly with the defendant. They suggested he should be impeached as well.

The select committee was set up last year at the behest of the pan-democrats after it emerged that Leung had received the money in 2011 after UGL bought insolvent property company DTZ, of which he was a director. Leung agreed under the deal not to form or join a rival firm, but he did not declare the payment to his cabinet, the Executive Council.

While Leung saw no conflict of interest from the start, the pan-democrats found new ammunition to attack him over the changes he made to Chow’s document, all 47 of which were traced to the user name “CEO-CE” on April 21.

Leung’s critics saw it as a bid to divert public attention from the more important issues and influence the investigation.

Leung confirmed on Tuesday that he had directly persuaded Chow to expand the lawmaker’s proposal on what the probe should look into, instead of the usual practice of approaching the Legco secretariat over such matters.

“I discussed with him, he agreed … and I passed him the document that I revised to include all [additional questions] and that document is now revealed,” Leung said.

Asked why he had dealt only with Chow, of the Democratic Alliance for the Betterment and Progress of Hong Kong, Leung said it was because he felt Chow “spoke more” during meetings and would be most likely to agree with him on expanding the boundaries of the investigation.

Leung tried to turn the tables on the committee, questioning how confidential information from the closed-door meeting on Monday could have been leaked to the public.

Speaking separately, Chow admitted that he should have been more forthcoming but denied any wrongdoing.

“I did not hide anything or break any rule,” he said. “As long as it would ensure fairness in an investigation, even a prosecutor would discuss with defence counsel on the agreed facts.”

Civic Party leader Alvin Yeung Ngok-kiu retorted: “Chow is not a defence lawyer in the committee. He should be representing Hong Kong people in investigating Leung.

“By taking the advice of the object of the probe without prior declaration … it shows that he is not fit to be a lawmaker.”

Democratic Party lawmaker Lam Cheuk-ting accused Chow of “simply trying to downplay his collusion with Leung”, while party colleague Andrew Wan Siu-kin said the case reflected “the executive branch’s unprecedented meddling with a Legco probe”.

They urged Chow to quit the committee and even Legco altogether, but Chow only said he would not “cling on to this post”.

Democratic Party lawmakers Ted Hui Chi-fung and Roy Kwong Chun-yu went a step further to lodge a complaint with the Independent Commission Against Corruption, alleging misconduct in public office.

Independent pan-democrat lawmaker Claudia Mo Man-ching and former legislator Gary Fan Kwok-wai of the localist group Hong Kong First also filed complaints with the graft buster.

More revelations of interference

Chief Executive Leung Chun-ying has never shied away from trying to exert influence on the operations of the Legislative Council – such as expressing his preference for key committee chairs, or setting the agenda for meetings – according to pro-establishment sources.

The revelation came as Leung admitted his hand in attempting to change the scope of a Legco probe into his receipt of a HK$50 million payment from Australian firm UGL.

Pro-establishment camp insiders told the Post it was not the first time Leung had exerted his influence in Legco.

One explicit example was in 2015, after moderate democrat Ronny Tong Ka-wah, deputy chairman of the House Committee, resigned as a lawmaker. Leung was very concerned about who was replacing Tong, sources said. Two individuals in the camp, speaking on condition of anonymity, confirmed that candidates Kenneth Leung Kai-cheong and Sin Chung-kai – both pan-democrats who had criticised Leung over the UGL saga – were not favoured by the chief executive to take the post.

The sources also revealed how Leung’s administration tried to influence discussions at Legco meetings.

“Some bureau officials would recommend suggested questions to us for panel meetings, because they were worried that no lawmakers would raise the targeted issues,” a source said.

The sources also revealed they were asked to raise easier follow-up questions to officials – who were grilled by pan-democrats – over the missing booksellers saga during weekly Legco meetings.

Back in 2014, pan-democrat “Long Hair” Leung Kwok-hung found a piece of paper in Legco with the words “follow-up questions provided by Security Bureau” written on it. The Democratic Alliance for the Betterment and Progress of Hong Kong admitted that the document belonged to them, but denied that the slip was provided by the bureau.

The chief executive’s office has not responded to the accusations.

Veteran pro-establishment lawmaker Wong Kwok-kin did not see the incidents as interference. “It is common for governments to collaborate with parties. Would you accuse Donald Trump of cooperating with the Republican Party?” he asked.

But Civic Party leader Alvin Yeung Ngok-kiu said Legco should be autonomous as there was no ruling party system in Hong Kong.

Additional reporting by Kimmy Chung