Hong Kong police have arrested 15 high-profile democracy activists on charges of illegal assembly.

The arrests took place just hours after China�s top representative office in the semi-autonomous city declared it is not bound by Hong Kong�s constitutional restrictions that bar Chinese government from interfering in local affairs.

Police arrested prominent figures, including the media tycoon Jimmy Lai and 81-year-old Martin Lee, the founder of the Democratic party and a senior barrister, in the biggest crackdown on the pro-democracy movement since the sometimes violent anti-government protests that have rocked the former British colony since June last year.

The 15 people arrested allegedly organised and took part in unlawful assemblies and police do not rule out that more will be arrested, Supt Lam Wing-Ho said.

Also among the detained were the barrister Margaret Ng, lawyer Albert Ho, labour rights activist Lee Cheuk-yan, former legislators Leung Kwok-hung and Au Nok-hin, and younger activists such as Figo Chan, the vice-convener of the Civil Human Rights Front, which organised several mass protests approved by police last year.

The 15 were accused of joining three unapproved protests on 18 August, 1 October and 20 October last year, local media reported.

Pro-democracy lawmakers say the arrests are an attempt to silence the movement after Chinese officials told Hong Kong to enact national security legislation. Claudia Mo said Beijing was also trying to �terrorise Hong Kong opposition� ahead of the legislative council election in September.

The veteran China watcher, Johnny Lau, said Beijing is trying to hit hard at Hong Kong while the world is busy dealing with Covid-19.

�In Xi Jinping�s eyes this is an opportunity to shuffle the cards and to assert its narrative,� he said. �If the foreign countries turn a blind eye and fail to rein in [China�s power], they would also suffer.�

The arrests came just hours after China�s liaison office asserted in a strongly-worded statement that it and the Hong Kong and Macau Affairs Office (HKMAO) � China�s top bodies overseeing the city�s affairs � are �authorised by the central authorities to handle Hong Kong affairs.�

Earlier this week, the liason office�s chief, Luo Huining, called for controversial national security laws to be urgently passed as accusations of overreach by Beijing into the city�s legislative council and judiciary escalate.

Hong Kong was promised a �high degree of autonomy� for at least 50 years after China resumed control in 1997, under the Sino-British joint declaration. The city�s post-handover mini-constitution, the Basic Law, bars the mainland Chinese government from interfering in Hong Kong affairs, and article 22 states that no department under the Chinese central and local governments �may interfere in the affairs which the Hong Kong special administrative region administers on its own in accordance with this law.�

But the liaison office statement, published late on Friday, asserts that �a high degree of autonomy is not complete autonomy.� It stresses that Hong Kong�s right to self-rule is �authorised by the central government.�

The statement argues that the liaison office and the HKMAO �are not what is referred to in article 22 of the Basic Law, or what is commonly understood to be �departments under the central people�s government�.� It adds that the offices derive their authority both from China�s constitution and the Basic Law.

This week, pro-democracy lawmakers accused the Chinese government of �blatant intervention� and violation of article 22 of the Basic Law after the HKMAO said some lawmakers were guilty of misconduct in public office for delaying bills, failing to appoint a House committee chairman and paralysing the legislature by filibustering.

The liaison office statement said people who made such allegations were distorting the Basic Law and misleading public opinion, adding that �loyalty to the country is a necessary requirement� for lawmakers.

China law expert Prof Jerome Cohen at the New York University descibed China�s statement is �astounding and incendiary�. Test and trace: lessons from Hong Kong on avoiding a coronavirus lockdown Read more

�If taken seriously, it collapses the whole one country, two systems edifice that was constructed over so many years since the joint declaration,� he said.

Prof Michael Davis, a global fellow at the Wilson Center and former law professor at the University of Hong Kong, said China�s aggressive language would �result in further pushback� from Hong Kong society, which has already experienced its most severe political crisis.

�The danger is that Hong Kong�s autonomy will be squandered and this has implications for all countries that have relied on the promises made to Hong Kong,� he said. �This fear that Hong Kong�s autonomy will be lost, along with it the rule of law, is what has driven the many protests in Hong Kong and international concern.�

Alvin Cheung, a legal scholar specialising in Hong Kong issues at New York University, said: �[The fact that] Beijing is not even pretending to keep up appearances heralds a dark new stage in Hong Kong�s post-1997 development � It suggests repression will intensify further.�

A Foreign & Commonwealth Office spokesperson said in a statement that the UK government was concerned about the arrests and stressed that the right to peaceful protest was �protected in both the joint declaration and the Basic Law�.

�It is essential that any protests are conducted peacefully, and that the authorities avoid actions that inflame tensions. The authorities should focus on rebuilding trust through a process of meaningful political dialogue,� the statement said.

Chris Patten, the last governor of Hong Kong, said while the world�s attention is focused on the covid-19 epidemic, Beijing has taken �yet another step towards burying one-country, two-system� and the arrests show that �Beijing is determined to throttle Hong Kong�.

He said the liaison office�s claim that it is not bound by the basic law is �a reckless argument which shows that Xi Jinping is determined to abandon the policies pursued by his predecessors, even at the cost of destroying Hong Kong�s way of life�.

�It should be rejected immediately by all those governments and parliaments around the world who know the importance of safe-guarding the high degree of autonomy which is guaranteed by the Basic Law.�

Lee, often dubbed the �Father of Democracy� in Hong Kong and a drafter of the Basic Law, said after he was released on bail that he had �no regrets� and felt �proud to walk the road of democracy with the outstanding youths in Hong Kong�.