The British government warned China on Thursday that there will be "serious consequences" if Beijing brakes the agreement that guarantees rights and freedoms in Hong Kong under the 'one country, two systems' principle.
British Foreign Minister Jeremy Hunt said he will not "swallow and move forward" if Beijing breaks the Sino-British Joint Statement signed in 1984.
"It is very important that the 'one country, two systems' approach is honored," he told the BBC.
"China is a country that has vastly benefited from an international rules-based system... Failure to honor this important agreement between the UK and China will certainly have consequences," for the two countries, he said.
China and Britain were embroiled in a diplomatic dispute this week after Beijing accused the British government of "gross interference" in Hong Kong affairs.
At a press conference at the Chinese embassy in London, the Chinese ambassador to the United Kingdom, Liu Xiaoming, attacked British ministers for openly defending the rights of protesters in Hong Kong.
"The UK Government has chosen to be on the wrong side," he said.
"There have been inadequate observations that not only interfere with Hong Kong's internal affairs, but have also supported violent offenders," he added.
The 1984 agreement guarantees Hong Kong a high degree of autonomy and protection of various freedoms, including an independent judiciary.
"Hong Kong is part of China, we recognize that," Hunt said.
"What I want to say is that there will be serious consequences if the legal agreement between the UK and China is breached," he said.
The minister recalled that the UK condemned all violence, adding that many demonstrators in Hong Kong were discouraged by some of the incidents.
On the 1st, hundreds of protesters broke windows and destroyed railing to enter the building housing the Hong Kong Legislative Council.
In the assembly chamber, where deputies meet in plenary sessions, they vandalized the region's shield with graffiti and hung a British colonial flag, referring to the period in which Hong Kong was under the sovereignty of the United Kingdom.
"I did not support the violence," Hunt said. "But the way to deal with this violence is not repression, it is through understanding the root of the protests," he added.
Mr Hunt said the UK has "good relations" with China and there is no reason for that to change, although acknowledging that Wednesday was a "difficult" day, referring to comments from the Chinese ambassador.
Liu Xiaoming asked London to refrain from any "interference" over its former colony.
"I think the relationship (between London and Beijing) has suffered from the interference of the British Government in Hong Kong," said the ambassador.
The ambassador recalled that Hong Kong is no longer under British colonial rule, triggering a reaction from British diplomacy, which considered the statements "totally unacceptable."
Hong Kong has for almost a month been the scene of protests against a proposed law that would allow the extradition of criminals to China.
Hong Kong's chief executive, Carrie Lam, decided to suspend discussions on the proposal, but declined to withdraw definitively, prolonging the demonstrations.
The meeting took place on the same day of the 22nd anniversary of Hong Kong's return to China.
Hong Kong and Macau were integrated into the People's Republic of China in 1997 and 1999, respectively, with the status of special administrative regions, under the formula 'one country, two systems', which ensures that the socialist policies in force in the rest of China do not apply to territories which enjoy a "high degree of autonomy," with the exception of Defense and External Relations, which are the exclusive competence of the Chinese central government.