Foreign secretary Dominic Raab said the Chinese government had broken its promises under the joint declaration and was undermining the high degree of autonomy Hong Kong was supposed to enjoy.
“Beijing’s imposition of new rules to disqualify elected legislators in Hong Kong constitutes a clear breach of the legally-binding Sino-British Joint Declaration,” Mr Raab said.
“China has once again broken its promises and undermined Hong Kong’s high degree of autonomy. The UK will stand up for the people of Hong Kong and call out violations of their rights and freedoms.
“With our international partners, we will hold China to the obligations it freely assumed under international law.”
Pro-democracy legislators in the former British colony resigned en masse on Wednesday after the government moved to remove four of them.
It came after China’s National People’s Congress Standing Committee passed a resolution saying those who support Hong Kong’s independence or refuse to acknowledge Beijing’s sovereignty over the region should be disqualified.
China has in recent months moved to clamp down on opposition voices in Hong Kong with the imposition of a national security law, after months of anti-government protests rocked the city.
Foreign minister Nigel Adams told MPs in the House of Commons that this was only the third time the UK government had declared a breach in the joint declaration since 1997 – but the second time in the last six months.
“Hong Kong’s people are left now with a neutered legislature,” he said. “China has yet again broken its promise to the people of Hong Kong. Its actions tarnish China’s international reputation and undermined Hong Kong’s long-term stability.”