Leung said in a Facebook post on Tuesday: “Lam and others have used crowdfunded money (other people’s money) to harass me, so I would not preclude using the [same tactic] … against them. This is only fair and square.

“The NCA has concluded there was ‘no offence committed in Britain’ and cleared all the allegations – that is a slap to the face of Lam Cheuk-ting.”

Academics accuse former Hong Kong leader CY Leung of using lawsuits to intimidate opposition and suppress free speech

Lam launched what he called a “wolf-hunting action” against Leung in April along with fellow Democratic Party lawmaker Andrew Wan Siu-kin and other party members. The group hoped to help uncover fresh evidence and spark an overseas investigation against the former leader.

Since 2014 Hong Kong’s Independent Commission Against Corruption has been investigating Leung’s payment from UGL, which was made while he was the city’s leader between 2012 and last year.

Former Hong Kong leader CY Leung says Britain’s National Crime Agency is not investigating him over HK$50 million UGL deal

Leung, now a vice-chairman of China’s top political advisory body, the Chinese People’s Political Consultative Conference, struck the lucrative agreement three weeks after UGL made a bid to acquire DTZ, a property services company once listed in Britain, of which he was a director. As part of the bargain, he agreed not to form or join a rival firm and to help promote the company.

The soon-to-be chief executive resigned from DTZ’s governing board eight days prior to reaching the HK$50 million deal with UGL. Leung claimed the payment was a “golden handshake” and has repeatedly denied it involved any provision of services in favour of UGL.

He received part of the sum after becoming the city’s chief executive in 2012. But he did not declare it to his quasi-cabinet, the Executive Council, sparking concerns over a possible conflict of interest.

Lam’s crowdfunding campaign eventually raised over HK$2 million from more than 6,000 donors. Leung’s legal team meanwhile issued two letters against Lam in April over their claims concerning the UGL case.

The NCA last week said it would not investigate the matter, citing insufficient evidence.

“The alleged offences took place in Hong Kong, with no offence committed in the UK, and as such it is not a matter for the NCA,” the agency said.

The NCA’s updated reply on Tuesday to the Post however indicated that the complaint against Leung did not fall into the purview of the NCA.

“The alleged offences either did not occur in the UK, or are not matters for the NCA,” an NCA spokesperson said on Tuesday.

Lam’s lawyer Paul Harris had already conceded that the evidence might not be sufficient to press charges, but said British authorities should nevertheless look into how UGL and Leung signed their agreement.

TVB warned over ‘inaccurate’ reports on ex-Hong Kong leader CY Leung’s HK$50 million UGL deal

On Tuesday he said he would consider suing Lam for “malice”, but was not clear on whether that meant a libel lawsuit with a claim of malicious intent.

Such a case would be the third libel action the former chief executive has launched against his political rivals. His lawyers have issued letters over six other incidents, though Leung eventually did not pursue these cases.

Leung’s office did not respond to a Post inquiry.

Lam on Tuesday said he was not worried about being sued as the “public would be the best judge”.

He has been in London on a duty visit for Hong Kong’s legislature, where he earlier met British politicians. Lam and Wan urged lawmakers in the country to pursue the case, and said they would also consider following up in Australia, where UGL is based.