“I cannot stop them unless they say things to attack others or they violate the principles that are agreed before the meeting.”

His declaration came as Hong Kong’s Occupy protest zones remained peaceful on Sunday, following a night of violent clashes in Mong Kok that left 20 people injured.

Some 50 protesters were today manning the site in Mong Kok, where last night police used pepper spray and batons to control a crowd several hundred-strong.

Violence flared after midnight following an online call for protesters to block the junction of Argyle Street and Nathan Road.

While police this morning maintained that just three protesters and one policeman had been injured in the scuffles, the government put the figure at 20, according to AFP news agency.

However, Dr Au Yiu-kai, the medical team head with Occupy Central with Love and Peace, said his team treated 13 injured protesters during the clashes early on Sunday morning.

“Seven of them sustained injury to their heads with blood streaming down their faces. The police were hitting them with their batons. That was not minimum force as the police have claimed,” Au said.

“Some of them refused to get treated in the hospital because they feared they would get arrested. Hitting people with [a] police baton can cause concussion and fracture their skull. It could be fatal,” he added.

Last night’s ugly scenes came as the Occupy demonstration, calling for increased democratic rights, entered its fourth week.

Despite diminished numbers of protesters on the streets – tens of thousands poured onto the city’s highways at the start of Occupy Central – the protests are continuing to make headlines around the world.

Later today the Hong Kong Overseas Alliance (HKOA) will hold a rally in Green Park, London, to condemn what they say is an excessive use of force against the mainly young protesters.

A spokesman for the organisation, which attracted 4,000 people to a rally in support of Hong Kong outside the London’s Chinese Embassy on October 1, said the HKOA expressed its “deep regrets” over the police handling of the ongoing protests.

“The Hong Kong police are paid by the taxpayers to keep them safe not to bully them. These days, many Hongkongers have been calling Hong Kong police ‘public security police’ - that is the mainland Chinese police who are known to be heavy-handed with their own people,” the organisation said in a statement.

Hong Kong Labour Party member Cyd Ho said on RTHK’s Letter to Hong Kong this morning that the Occupy movement had been successful in giving Hongkongers a greater appetite for politics, which would continue even after the protest zones finally vanish.

A 23-year-old man in Tin Shui Wai on Saturday night became the first to be arrested for calling on others to join the Occupy protests since the civil disobedience movement began on September 28. Police said he had posted messages on an online forum to encourage others to join the demonstrations in Mong Kok.

Police arrested him for accessing a computer with criminal or dishonest intent, as well as for unlawful assembly after finding he had joined the protest on October 17. He has subsequently been released on bail and investigations are still ongoing, police said.

Asked if it is an offence to encourage others to join occupy protests on social media, public relations bureau chief superintendent Steve Hui Chun-tak, speaking at a regular press conference on Sunday, did not give a direct answer and would only provide a description of what the suspect said online.

“He was inciting others to join an unlawful assembly in Mong Kok, to charge [the] police cordon line and to paralyse the railway,” Hui said. “These amount to incitement of a very serious nature, and therefore we made the arrest.”

Hui reiterated that most laws that apply to the real word are applicable to the cyberspace as well, and that the force would make arrests if they had adequate evidence.

In Mong Kok this afternoon, the junction of Nathan Road and Argyle Street remained under the watchful eye of police officers, who reclaimed it from protesters in a major operation on Friday.

For some the mood was one of despondency, with several admitting they did not hold out hope that talks between the Federation of Students and the government would be productive.

Pitt Butt, 26, who spent Saturday night at the site, said he thought the meeting would come to nothing, and voiced his concerns about the policing methods employed in recent days.

"I was here last night and the police were hitting the protesters on their heads and arms with their batons. But the protesters were not doing anything.

"The police are like strangers to me now. I never thought that they could do such things to the people."

Graduate of Lingnan University, Kwok Hin, 20, said he had no faith in the host of Tuesday’s debate.

"I still remember that when some people stormed inside the Civic Square last month, there were Lingnan students among them. But the president did not say if the university would help bail them out," said Kwok, 20.

In Admiralty about 300 tents remained in the Occupy zone. Families wandered among the tents talking to protesters.

Frank Lee, 37, who works in the education sector, had decided to take his three-year-old daughter to the site.

"I support the students, their views and stances, and decided to bring her - even though she might not understand much - to make her aware of what's going on and take some iconic photos," he said, adding that the violence seen in recent days could only be halted with appropriate political action.

"It's not up to the students or even the police. After all, the ultimate responsibility belongs to the government, I mean to CY Leung. This can only be solved by political means,” he said.