Britain, along with the United States, Australia and Canada, has criticised China for the new law, saying it would breach the 1984 Sino-British agreement on Hong Kong and threaten its freedoms.

Beijing has said its decisions on national security in Hong Kong are its own affair and that Britain's link to the territory stemmed from "aggressive colonisation and unequal treaties".

In a six-monthly report on Hong Kong, covering events from July 1 to December 31 last year, foreign minister Dominic Raab said: "The solution to this unrest and its underlying causes must come from Hong Kong, and cannot be imposed from mainland China".

"Britain says the way through the current situation in Hong Kong is clear: all sides must invest in dialogue and reconciliation, underpinned by a robust, independent inquiry," he added.

Britain has pledged to give British National Overseas passport-holders in Hong Kong a path to British citizenship, allowing them to settle in the United Kingdom.

There are about 350,000 holders of BNO passports in Hong Kong and a further 2.5 million are eligible for them, the British government has said.

"There is still time for China to re-consider, to step back from the brink and respect Hong Kong's autonomy and respect its own international obligations," Raab wrote in a foreword to the report.