The Chinese ambassador to London has accused Britain of being two-faced in its approach to Hong Kong – pretending to be even-handed in the face of the violent demonstrations, but in reality supporting the demands of the protesters.

He also said UK politicians, including the foreign affairs select committee, were fanning the flames of unrest by referring to violent demonstrators as pro-democracy protesters.

The ambassador, Liu Xiaoming, at his third press conference on the Hong Kong crisis, said: “We have made our position known to the British side when they have made irresponsible remarks on Hong Kong. I think when the British government criticise Hong Kong police, criticise the Hong Kong government in handling the situation, they are interfering into China’s internal affairs. They look like they are balanced but as a matter of fact they are taking sides. That is our position.”

He continued: “Some western countries have publicly supported extreme violent offenders, the US House of Representatives adopted the so-called Hong Kong human rights and democracy act to blatantly interfere in Hong Kong affairs, which are China’s internal affairs.”

He added: “The British government and the foreign affairs committee of the House of Commons published China-related reports making irresponsible remarks on Hong Kong. What is worse, certain British politicians even planned to present [an] award to a chief propagandist for Hong Kong independence,” he said, in a reference to the planned presentation of the Westminster Award for Human Life, Human Rights and Human Dignity to pro-democracy campaigner Joshua Wong.

The Foreign Office in a statement said it was seriously concerned by events, and added it was vital that demonstrators who were injured were able to receive appropriate medical treatment, and “safe passage is made available to those that wish to leave the area”.

It called for “an end to the violence and the resumption of meaningful political dialogue ahead of the local elections this weekend”.

The Chinese ambassador also warned that if the protesters overstepped the mark with what he described as their “black terror”, it would be the end of the “one country, two systems” that marks Hong Kong’s relations with mainland China.

“If the violence continues the future of Hong Kong could be unimaginably dreadful,” he said. Already, “the fragrant harbour is sliding into the abyss of chaos”.

The true agenda of the protesters, he said, was the independence of Hong Kong from the motherland, a demand that would never be met by China.

“The Hong Kong government is trying very hard to put the situation under control,” Liu said. “But if the situation becomes uncontrollable, the central government would certainly not sit on our hands and watch. We have enough resolution and power to end the unrest.”

Liu was speaking after some of Hong Kong’s worst scenes of violence in in five months of protests, which led the British government to call for restraint on both sides.

China’s senior diplomat said: “For the past five months, the self-labelled peaceful protesters have resorted to senseless beating, smashing and arson. They have carried out premeditated attacks against police officers and a failed assassination of a member of the legislative council.” This was a reference to the stabbing of Junius Ho, a pro-Beijing Hong Kong lawmaker.

He interrupted the briefing to show a video of violent scenes over the past few months.

The ambassador said it was not yet necessary either to cancel next week’s local elections or to call in the Chinese army, saying the Chinese government still had faith in the leadership of the chief executive.

He said the army was already in Hong Kong. The solution, he repeatedly said, was to punish those responsible for the violence.

Liu accused pro-democracy protesters of creating trouble in front of the Chinese embassy in London last week, painting Hong Kong independence slogans on on both sides of the gate, as well as pushing the territory’s justice minister, Teresa Cheng, to the ground. The Metropolitan police have opened an investigation into the incident.