A British barrister who has come under fire for agreeing to prosecute prominent Hong Kong democracy activists has pulled out of the case, the SAR government announced on Wednesday.

Queen's Counsel David Perry had agreed to lead the protest-related case against a number of high-profile activists, including media tycoon Jimmy Lai and lawyers Martin Lee and Margaret Ng.

But Perry's decision was greeted with dismay in some quarters.

Among the critics was British Foreign Minister Dominic Raab who said he couldn't understand how anyone in good conscience could take up such a case, adding that people would regard the move as being "pretty mercenary".

Raab, a former lawyer himself, also said that getting Perry to take up the case was a "serious PR coup" for Beijing.

But Hong Kong's Department of Justice (DOJ) said on Wednesday that Perry is no longer involved in the prosecution, saying he "expressed concerns about such pressures and the exemption of quarantine, and indicated that the trial should proceed without him."

In a statement, the DOJ said another counsel has been instructed to take over the prosecution which relates to an alleged unauthorised assembly on August 18, 2019.

The DOJ also complained that some of the "ill-informed criticism" levelled against Perry had "conflated the matter with the national security law".

"As legal proceedings are still ongoing, it is inappropriate for anyone to comment on the case as it is a matter of sub judice. No one should embark upon baseless speculations," the department warned.