Boris Johnson has offered up to three million Hong Kong residents the right to settle in the UK and ultimately apply for citizenship after accusing China of a “clear and serious breach” of a key treaty with Britain.

The Prime Minister on Wednesday accused Beijing of violating the former British colony’s degree of autonomy by imposing a much-criticised national security law on the territory.

Mr Johnson said the move was a breach of the Sino-British Joint Declaration that aimed to smooth the transition when the territory was handed back to China in 1997.

In response, he told MPs he would introduce a new route for people in Hong Kong with British National (Overseas) (BNO) status to apply for visas to live and work in the UK and apply for citizenship.

Downing Street said they will be eligible to travel to the UK immediately ahead of the details of the scheme being finalised “in the coming weeks” and that they will not face salary thresholds.

Taking effect on Tuesday night, the security law in Hong Kong makes activities deemed subversive or secessionist punishable by imprisonment, and is seen as targeting anti-government demonstrators.

During Prime Minister’s Questions, Mr Johnson told the Commons: “The enactment and imposition of this national security law constitutes a clear and serious breach of the Sino-British Joint Declaration.

“It violates Hong Kong’s high degree of autonomy and is in direct conflict with Hong Kong Basic Law.

“We made clear that if China continues down this path we would introduce a new route for those with British National (Overseas) status to enter the UK, granting them limited leave to remain, with the ability to live and work in the UK and thereafter to apply for citizenship – and that is precisely what we will do.”

Mr Johnson’s commitment came after Hong Kong police made their first arrests under the new law, including one person said to have displayed a sign with the Union flag which called for Hong Kong’s independence.

Foreign Secretary Dominic Raab accused Beijing of a “grave and deeply disturbing” breach of the treaty which “threatens the strangulation” of Hong Kong’s freedoms.

He told MPs the “bespoke” new arrangement to be implemented in the coming months would grant BNOs five years’ limited leave to remain in the UK with the ability to live and work.

They would then be eligible to apply for settled status and would be able to apply for citizenship after 12 months with that status.

He said there would be no quotas on numbers. As of February, there were nearly 350,000 BNO passport holders, while the Government estimates there are around 2.9 million BNOs living in Hong Kong.

More than 70 arrests were made in Hong Kong on Wednesday, which marked 23 years since the handover.

Mr Johnson is under pressure from across the political spectrum to take a firmer stance against Beijing, including over the role of Chinese firm Huawei in the UK’s 5G network.

Shadow foreign secretary Lisa Nandy said the UK should not rely on China for 5G or investment in nuclear power.

“We need far greater strategic independence from China, which means that we need to have home-grown alternatives for our 5G network and our nuclear power,” she told Times Radio.

“I don’t think we should be handing over large chunks of our energy infrastructure, especially our nuclear energy infrastructure, to a country that’s behaved in such an aggressive way towards the UK and the people of Hong Kong in recent weeks.”

Mr Raab was also facing calls to act over the breach of the 1985 Sino-British Joint Declaration, the legally binding agreement to give Hong Kong a high level of autonomy for at least 50 years.

Chinese ambassador Liu Xiaoming was summoned to the Foreign Office on Wednesday where permanent secretary Sir Simon McDonald said the imposition of the legislation breaches the Sino-British Joint Declaration, it is understood.