Sumption recently claimed in an opinion piece and interviews that Hong Kong was “slowly becoming a totalitarian state” and that the Beijing-decreed national security law had been suppressing dissent.

He also said that having overseas judges to help sustain the rule of law in Hong Kong was “no longer realistic”.

A spokesman for Beijing’s liaison office in Hong Kong sharply criticised Sumption for “publicly smearing” the city’s rule of law, judiciary and local judges and said that his attempts to spread rumours were unethical.

“He blatantly violated the principle of not commenting on pending cases, attacked the judgments of fellow judges, made unreasonable comments on the judgments of pending cases and violated the professional ethics of judges,” the spokesman said.

He also accused Sumption of violating his oath of office as a non-permanent judge by slandering the legitimacy of the top national legislative body in enacting and interpreting the national security law.

“Jonathan Sumption’s absurd remarks deviated from judges’ ethics and professionalism and were in line with the attacks on Hong Kong’s rule of law by external forces,” he said.

“That fully demonstrates that he is willing to serve as a tool for British political manipulation and has completely become a tool for external forces to interfere with and undermine Hong Kong’s security and stability.”

Sumption, 75, and British judge Lawrence Collins, 83, announced their resignations from the Court of Final Appeal last Thursday, with the latter also citing the “political situation” in Hong Kong as the reason for his departure.

“Jonathan Sumption’s absurd behaviour that deviates from professionalism and lacks moral integrity will eventually become a stain in his life that would be hard to wash away,” the office said.

The late evening statements were made a day after the Hong Kong and Macau Affairs Office posted a commentary on its WeChat channel under the pen name of “Gang Ao Ping” that called Sumption a “disgrace to the legal profession” for “utterly abandoning professionalism and ethics”.

The office posted another commentary under the same name on Friday evening, which said “the sound of buzzing flies cannot disrupt people’s firm confidence in Hong Kong’s rule of law”.

While the previous piece was filled with strong language, the second cited the city’s place in international rankings, as well as statistics, to show the reputation of Hong Kong’s legal system had continued to draw talent and capital.

“The people’s confidence in Hong Kong’s rule of law is rock solid, and this cannot be shaken by a few articles or a few noises ... maybe [Sumption] can wake up and find his way back,” the commentary said.

Barrister Ronny Tong Ka-wah, a member of Hong Kong’s key decision-making Executive Council, said he was shocked by Sumption’s “antics” of “baseless attacks” on the rule of law of Hong Kong, which he believed should not go unanswered.

“I don’t think at this stage being nice to anyone would earn us any points,” he said. “If we don’t defend the actual situation in Hong Kong, [do] you think judges will dare come and be part of a ‘charade’ to ‘beautify’ an ‘unjust regime’? I doubt it.

“We are between a rock and a hard place and were placed there by the vocal antics of Sumption.”

Veteran political commentator Johnny Lau Yui-siu said Beijing felt a need to “stop the bleeding” with strong rebuttals after Sumption openly went against authorities’ aim to boost the reputation of Hong Kong’s rule of law.

“Sumption has also said before that he thinks Hong Kong’s judiciary can be maintained,” Lau said. “Now that the overall favourability of Hong Kong’s judicial system has deteriorated, Beijing feels that there is another set of political forces behind it. That’s why Beijing is accusing Sumption of giving in.”

The former United Kingdom Supreme Court judge has been no stranger to controversy in recent years – his rejection of London’s lockdown measures imposed during the Covid-19 pandemic and support for Britain to leave the European Convention on Human Rights have both drawn critics.

Simon Young Ngai-man, a law professor at the University of Hong Kong, said he believed Sumption’s actions had been “so unusual and exceptional” that it called for a strong response to balance “what would otherwise be the projection of a distorted picture of the situation in Hong Kong”.

“It’s not likely that others would follow suit, [so] we shouldn’t have to worry about the effects of the strong response on this occasion,” he added.

Hong Kong, the only common law jurisdiction in China, is permitted to recruit judges from elsewhere under its mini-constitution, the Basic Law. The tradition is seen as an indicator of confidence in the city’s rule of law.

Another Court of Final Appeal judge, Canadian Beverley McLachlin, 80, announced on Monday that she would retire once her term ended this summer, saying she intended to spend more time with her family.

But she added she continued to have confidence in the members of the court, their independence and their determination to uphold the rule of law.

Her departure would mean there would soon only be seven overseas non-permanent judges sitting on the city’s top bench.