A man bailed by a UK court last week over allegations of assisting Hong Kong's intelligence services in a Chinese-linked espionage case has been found dead, police said on Tuesday.

Matthew Trickett, 37, was found dead in a park in Maidenhead, west of London, on Sunday following a report by a member of the public, Thames Valley Police said.

"An investigation is ongoing into the death, which is currently being treated as unexplained," the force said in a statement.

Trickett, from southeast England, was one of three men accused in the Hong Kong spy case.

He was released on bail along with Chi Leung Wai, 38, and Chung Biu Yuen, 63, pending their next court appearance which was scheduled to take place on Friday.

The three were all charged with assisting a foreign intelligence service and also with foreign interference, in violation of the 2023 National Security Act.

The act came into force in December and is designed to bolster UK national security against so-called "hostile activity" targeting the country's democratic institutions, economy and values.

Police said earlier the "foreign intelligence service" in question was Hong Kong's.

The charges prompted a strong response from Beijing.

China's foreign affairs commissioner in its territory of Hong Kong "strongly condemned" Britain for "cooking up charges" and accused it of a "vicious intention to interfere" in Hong Kong's affairs.

The office warned that Britain would receive "China's firm and strong retaliation".

 China spying charges 

 The UK has been outspoken about the Hong Kong government's new national security law, which it views as eroding the territory's rights and freedoms.

Britain has repeatedly denounced the treatment of pro-democracy campaigners in its former colony, and launched a visa scheme to allow Hong Kong residents to come to the UK.

As a result, it has become a refuge for dissidents, including pro-democracy politician Nathan Law.

Hong Kong police last year issued a wanted list of eight overseas activists that included Law.

As part of the UK police investigation, 11 people were taken into custody earlier this month.

The case involving Trickett comes after two men, one of whom works in the UK parliament, were last month charged with spying for China. They are due to be tried next year.

Former prime minister David Cameron, now foreign minister, in 2015 hailed a "Golden Age" of ties between London and Beijing, but relations have deteriorated significantly in recent years.

As well as Hong Kong, the two countries have clashed over the treatment of the Uighur Muslim minority in China's Xinjiang region and over human rights in Tibet.

Amnesty International said in a recent report that China was targeting citizens studying abroad for their political activism, with some students reporting harassment of family members back home.

Asked about the Amnesty report, Beijing's foreign ministry dismissed it as "purely malicious smears".