Beijing’s imposition of new rules disqualifying opposition legislators in Hong Kong constitutes a breach of legally binding international commitments, the UK foreign secretary, Dominic Raab, has said. Raab said the move represented a “clear breach” of the Sino-British joint declaration, which was supposed to guarantee Hong Kong a high degree of autonomy under Chinese rule. In a statement, Raab said the UK would work with allies to hold the Chinese government to its obligations under international law. “China has once again broken its promises and undermined Hong Kong’s high degree of autonomy,” said Raab. “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.” A measure passed by China’s highest legislative body on Wednesday allowed the disqualification of “unpatriotic” opposition members in Hong Kong’s parliament and prompted the entire pro-democracy caucus to announce their resignation. The move is likely to signal fresh sanctions on Chinese and Hong Kong officials, probably in cooperation with the US. The UK said the decision to disqualify Hong Kong legislators was “part of a pattern apparently designed to harass and stifle all voices critical of China’s policies”. The new rules for disqualification provide a further tool in this campaign, with vague criteria open to wide-ranging interpretation. The Chinese actions breached both China’s commitment that Hong Kong would enjoy a “high degree of autonomy” and the right to freedom of speech guaranteed under paragraph 3 and annex I of the declaration, the Foreign Office said. The Foreign Office, under pressure from politicians from all parties, is expected to go ahead with sanctioning at least four Hong Kong officials shortly, but will not discuss details since they do not want to give advance notice to anyone liable to be affected. In the Commons the Foreign Office minister Nigel Adams, replying to an urgent question, said the Chinese ambassador was being summoned to hear the UK government’s concerns and to demand that China uphold its international obligations. Adams, the minister for Asia, said: “We will continue to consider designations under our Magnitsky-style sanctions regime.” He was asked by MPs if Britain would sanction Hong Kong chief executive, Carrie Lam, and said it would not be helpful to speculate on names at this stage. It is the third time since 1997 and the handover of Hong Kong to China that the UK has asserted a breach of the joint declaration. The first breach according to the British was in 2006. The second was in June 2020 when Beijing introduced the Hong Kong national security legislation. In March 2016, the former prime minister John Major visited Hong Kong and warned: “If there were any suggestion of a breach of the joint declaration, we would have a duty to pursue every legal and other avenue available to us.” But in practice the legal routes open to the UK to challenge Beijing are limited to rhetorical denunciation and sanctions against individual Chinese leaders or Hong Kong legislators. The Sino-British joint declaration itself does not have a mechanism endorsed by both parties to ensure its compliance. Even though the agreement is registered with the United Nations, it did not include mechanisms of supervision by the UN. Therefore, only the signatories of the declaration have the right to raise any potential terms violations. The main two courts to which the UK could appeal would either be the international court of justice or to a binding third-party permanent court of arbitration, a body that operates outside the UN ambit. The US national security adviser, Richard O’Brien, said on Wednesday Beijing’s recent actions disqualifying pro-democracy legislators from Hong Kong’s legislative council left no doubt that the Chinese Communist party (CCP) had “flagrantly violated its international commitments”. He added that the United States would continue “to identify and sanction those responsible for extinguishing Hong Kong’s freedom”. On Monday, the United States imposed sanctions on four more officials accused of curbing freedoms in Hong Kong while vowing accountability over China’s clampdown in the city. The European Union said it would look at further measures against China by the end of the year. In a statement the EU said: “These latest steps constitute a further severe blow to political pluralism and freedom of opinion in Hong Kong.”