The lawyers called the jail terms “a serious threat” to the rule of law and the “one country, two systems” principle under which Hong Kong is governed.

Wong and Law were originally given community service orders, and Chow a suspended jail sentence, for unlawful assembly. But they were eventually jailed after the Department of Justice took the trio back to an appeal court, demanding stronger punishments.

Jailing of Hong Kong Occupy trio a ‘serious threat’ to city’s rule of law, top foreign lawyers say in joint letter

Lam said on Tuesday: “The Department of Justice has issued a comprehensive response, and I have little to add. Basically, our response is that the joint letter shows that the signatories misunderstood the case and lacked understanding of Hong Kong’s judicial system.”

But in a 790-word response, a spokeswoman for the Department of Justice wrote: “The joint letter’s comments on judicial independence are totally unjustified … The judiciary remains truly independent and has displayed very high quality in its discharge of professional duties.”

Hong Kong leader Carrie Lam says she prays for city’s youth daily, warns them to ‘think thrice’ before breaking law

Justice Secretary Rimsky Yuen Kwok-keung has yet to respond to the letter. But at a forum for secondary school pupils organised by the Law Society on Sunday, he was asked if Beijing had been behind the jailing of Wong, Law and Chow.

“Categorically and very clearly, I can tell you that the [central government] was absolutely not involved,” Yuen said.

In the joint letter, the 12 lawyers said they regarded the imprisonment of the trio as “a breach of the principle of double jeopardy”, under which a person who has been acquitted or convicted of a crime will be spared any further prosecution for the same offence.

Former University of Hong Kong law dean Johannes Chan man-mun on Tuesday said that claim was inaccurate.

“The only inaccuracy I find in this letter is the concept of double jeopardy,” he said.

“In the strictest term, it’s not [double jeopardy]. It’s just an appeal for the same case. An appeal is not considered double jeopardy.”

But Chan noted that legal professionals and academics had expressed concern over whether the Court of Appeal deviated from the judgment of the facts put forward by the judge in the lower court.

“I hope the government has a more open-minded attitude but not a defensive one by saying that they [the signatories] don’t understand double jeopardy and they’re wrong,” Chan said.

“I think the main point is not whether Hong Kong’s judiciary can be independent. It’s how Hong Kong’s judicial independence is under pressure and influence from Beijing.”