Officials from the central authorities and the Hong Kong Special Administrative Region have condemned the United Kingdom for making unjustified accusations about Hong Kong.

On Monday, British police arrested three men for allegedly assisting Hong Kong's foreign intelligence service. One of those arrested is Yuen Chung-biu, an office manager at the Hong Kong Economic and Trade Office in London.

The trio appeared at Westminster Magistrates' Court on Monday, charged with offenses under the UK's National Security Act. They have been released on bail, with the next hearing to be held on May 24.

At a regular news conference on Tuesday, Hong Kong Chief Executive John Lee Ka-chiu said any unjustified accusation against Hong Kong is "unacceptable".

He said the Hong Kong government has demanded the British Consulate General in Hong Kong provide full details of the matter, saying that the role of the Hong Kong Economic and Trade Office is to enhance overseas people's understanding of Hong Kong's economic and cultural advantages.

Hong Kong has established 14 economic and trade offices overseas, including four in Europe — in Berlin, Brussels, Geneva and London. Lee said the Hong Kong government had asked the UK government to handle the matter impartially, and ensure the normal operation of the office in London is not affected.

Any interference with the work of economic and trade offices goes against the principles of free trade and free economy, and such actions will only bring negative impacts to the UK economy, Lee said.

The Ministry of Foreign Affairs expressed grave concerns about the issue on Tuesday, with spokesman Wang Wenbin urging the British side to earnestly protect the legitimate rights and interests of Chinese citizens in the UK.

Wang said the UK has staged a series of accusations against China, including ones about "China spies" and cyberattacks. All the accusations are groundless and slanderous, he said.

On Monday, the Chinese Embassy in the UK strongly condemned what it labeled as the UK's malicious fabrication and unwarranted accusation against Hong Kong.

The British authorities had harassed, arrested and detained Chinese citizens in the UK under the pretext of national security, constituting a grave provocation against China and severely contravening the basic norms governing international relations, the embassy said in a statement.

It urged the UK to immediately correct its wrongdoing, emphasizing that any political trick to divert public attention and cover up its own serious problems by smearing China is doomed to fail.

Also on Monday, the Commissioner's Office of the Chinese Foreign Ministry in the Hong Kong Special Administrative Region strongly condemned the British side for what it described as trumped-up charges, the arbitrary arrest of Chinese citizens and the slandering of the Hong Kong government.

An office spokesperson said that under the pretext of national security, the British side had ignored basic human rights and made arbitrary arrests and detentions, which was not only against the spirit of the rule of law, but also naked political manipulation.

The UK must stop interfering in Hong Kong affairs and China's internal affairs, otherwise, the Chinese side will take resolute countermeasures, the spokesperson said.

Lau Siu-kai, a consultant to the Chinese Association of Hong Kong and Macao Studies, said the incident might develop into "a diplomatic storm" between China and the UK as the charges against the trio are serious.

Lau said he believes there is no reason for the Hong Kong government to engage in espionage in the UK.

Regina Ip Lau Suk-yee, convener of Hong Kong's Executive Council and a former secretary for security in Hong Kong, said she was surprised and shocked by the UK's accusation.

Ip said the National Security Act passed by the UK parliament in July is regarded as very stringent and includes broad but vague definitions. She said the Hong Kong government should lodge serious representations to the UK authorities, seek to find out whether they have reasonable grounds to target Hong Kong, and provide legal aid to the Hong Kong people involved.