British Prime Minister Boris Johnson has said that he will offer millions of Hong Kong residents passports and access to British citizenship if China insists on imposing its national security law on the region.

For its part, the British Times newspaper said that the British National Security Council agreed to reconsider the UK's relationship with China.

"Many in Hong Kong fear that their lifestyle - which China has vowed to keep - is under threat," Johnson wrote in an article published in the Times and the South China Morning Post.

"Hong Kong is successful because its people are free ... if China goes ahead, this will be a direct conflict with its obligations under the joint declaration, that legally binding treaty registered with the United Nations," he said.

He stressed that "if China goes ahead and gives a justification for these concerns, Britain cannot by its conscience ignore the matter and overlook it, on the contrary, we will respect our duties and offer an alternative option."

Johnson said that about 350,000 people in Hong Kong currently hold the "British Overseas Passport" which allows entry into the UK without a visa for up to six months.

An additional 2.5 million people will be eligible to apply for this document which was granted to residents of the former British colony when returned to China.

Protester raises British passports during protests in Hong Kong against the National Security Act (Getty Images)

Law and penalties

The law on national security - which the Chinese People's National Assembly approved the principle of imposing but not yet completed - provides for sanctions for separatist, "terrorist", sabotage and foreign activities in the semi-autonomous Chinese region.

Beijing decided to impose this law after a wave of pro-democracy demonstrations, which sparked international opposition and led to the return of the unrest to Hong Kong.

Opponents of Beijing's influence fear that this could lead to an unprecedented decline in freedoms in the financial center of seven million people.

As part of the international protests against Chinese law, London has announced plans to grant more rights to Hong Kong residents who hold a "British overseas passport".

The National Security Act provides penalties for separatist and "terrorist" activities (Getty Images)

Call and reject

For his part, British Foreign Secretary Dominic Rapp on Tuesday called on Beijing to reverse its decision.

"It is time for China to think and move away from the brink and respect Hong Kong's autonomy and its international obligations," he said in Parliament.

But Johnson's personal intervention greatly increases pressure, he wrote, "I hope this will not be reached," stressing that "Britain is not seeking to block the rise of China" among nations.

"Precisely because we welcome China as a leading member of the global community, we expect it to abide by international agreements," he added.

The British Prime Minister rejected the accusations that London organized the protests, saying that "Britain wants nothing more than the success of Hong Kong under the banner of one country, two systems."

He expressed the hope that China would like "the same thing" and said, "Let's work together to achieve this."

In contrast, the Chinese Foreign Ministry said that Britain has no legal authority to supervise or interfere in Hong Kong.

The Chinese Foreign Ministry added that any threat to Hong Kong's stability comes from foreign powers.