The editorial in question called on newly elected lawmakers to invoke the Legislative Council’s special powers to pursue Leung over the controversial payment of HK$50 million he ­received from Australian firm UGL before he took office in 2012.

“The usage of the false corruption allegation to prevent Mr C.Y. Leung from exercising his constitutional right to stand for the ­re-election ... if he chooses to, demonstrates the very serious kind of malicious and injurious motive.”

The chief executive has yet to confirm whether he will seek a second term, but this is the clearest indication yet that he has it in mind.

Apple Daily published the legal letter on its website on Thursday but a government source said that it omitted part of the letter stating that the UK Serious Fraud Office “has decided not to start an investigation” into Leung.

Leung has repeatedly denied wrongdoing over the deal with UGL in 2011, months before he became chief executive. The engineering firm had sought to buy out insolvent property firm DTZ, of which Leung was a director.

The deal – made two days ­before Leung resigned from DTZ and the completion of the takeover – stipulated that he would ­receive the money in two instalments in 2012 and 2013. UGL and Leung said the money was to prevent him from forming or joining a rival firm within two years. In an “additional commitment” clause, Leung agreed to “[act] as a referee and adviser from time to time” if UGL asked.

The Independent Commission Against Corruption has been looking into allegations of corruption over the deal.

In his legal letter, Leung quoted Chief Secretary Carrie Lam Cheng Yuet-ngor as saying it was not necessary to disclose the commercial arrangement.

The letter also objected to the paper’s “disdainful” use of nicknames for Leung such as “689”, “Wolf Ying” and “Liar Ying” in a campaign against his leadership.

The term “689” refers to the number of votes from the 1,200-strong election committee that put him in office in 2012.

Chan Pui-man, the paper’s chief editor, dismissed Leung’s complaint that the editorial could make him un-electable as “ridiculous and laughable”.

“If we could be so powerful, we would really feel honoured,” ­Apple Daily quoted her as saying.

The Journalists Association expressed “shock and regret” over Leung’s legal action, saying he was causing public concern over freedom of speech.

Chinese University political scientist Ivan Choy Chi-keung said Leung’s move would do no good to his public image.

This is the second time the city’s leader has threatened legal action against a local media outlet. In 2013, Leung issued legal letters to the Hong Kong Economic Journal and columnist Joseph Lian Yi-zheng over an article linking him to triad gangsters.

The newspaper printed an apology but insisted this was addressed to readers, not Leung, and said there would be no retraction.

In an interview with the Post earlier this year, Leung said Hong Kong had “very liberal libel laws” and the attacks he faced every day was “a part of life”.

“We don’t throw people behind bars because they attack the chief executive,” he said. “And I have been in this game for nearly 30 years now.”

Meanwhile, former pan-democrat lawmaker Ronny Tong Ka-wah, who now heads the Path of Democracy policy think tank, said he was invited to Shenzhen for a meeting with Feng Wei, deputy director of the State Council’s Hong Kong and Macau Affairs Office, last week.

Tong said he told Feng that Beijing should consider replacing Leung after his term expires next year. “I told Feng that Leung was not the man who could mend the social split currently affecting Hong Kong,” he said.

Tong declined to reveal Feng’s response, but said the mainland official appeared to understand the problem.