Britain will stand up to "Chinese aggression" and defend Hong Kong's freedoms, Prime Minister Rishi Sunak vowed Wednesday after his government intervened in the case of jailed media tycoon Jimmy Lai.

Minister for Asia Anne-Marie Trevelyan met the pro-democracy figure's legal team on Tuesday, prompting an angry response from the Hong Kong government.

But speaking in parliament, Sunak insisted on Britain's right to get involved in its former colony, whose civil liberties were meant to be guaranteed for 50 years under the Sino-UK agreement that came into effect in 1985.

The UK has admitted hundreds of thousands of Hong Kongers fleeing China's crackdown, he said, and it will remain "robust in standing up to what we believe to be Chinese aggression".

Britain would also resist the "undermining of the (50-year) settlement that we fought so hard to achieve".

Sunak was responding to China critic Iain Duncan Smith, who along with other MPs met earlier Wednesday with Lai's son Sebastien.

Jimmy Lai, 75, is a British citizen and founder of Hong Kong's now-shuttered Apple Daily newspaper.

He is facing up to life in prison for "colluding with foreign forces" -- a crime under the security law Beijing imposed on Hong Kong to quash huge democracy protests in 2019.

His trial, scheduled for December last year, was pushed to September after Hong Kong authorities asked Beijing to step in and bar Lai from being represented by a London lawyer.

"We've been clear that the Hong Kong authorities must end their targeting of pro-democracy voices, including Jimmy Lai," Sunak's spokesman told reporters after the Trevelyan meeting.

Hong Kong's government responded: "We will never tolerate, and strongly deplore, any form of interference by any foreign power or individual with the (territory's) judicial proceedings and internal affairs."

AFP