A researcher in Britain's parliament denied he was a Chinese spy on Monday, saying he was "completely innocent" of media allegations of working for Beijing and had only ever tried to educate others about China.
London's Metropolitan Police said on Sunday two men had been arrested in March under the Official Secrets Act. The Sunday Times reported one of them was a parliamentary researcher, and on Monday the Times published a picture of a man it said was him.
Opposition Labour leader Keir Starmer told parliament: "The news of the arrest of a researcher here in parliament on suspicion of spying for China is a serious breach of security conducted by the Beijing security services."
Lawyers for the man released a statement on his behalf without identifying him, denying the accusations.
"I feel forced to respond to the media accusations that I am a 'Chinese spy'. It is wrong that I should be obliged to make any form of public comment on the misreporting that has taken place," the man said in the statement.
"However, given what has been reported, it is vital that it is known that I am completely innocent. I have spent my career to date trying to educate others about the challenge and threats presented by the Chinese Communist Party."
The two suspects have been released on police bail until early October, the police said. The second man has not commented publicly.
Following typical practice in Britain, police have not identified the suspects, who have not yet been charged.
The arrests are yet another blow to relations between Britain and China that ministers had hoped to revive after being strained by tensions over security, investment and human rights.
British Prime Minister Rishi Sunak told reporters he had raised "his very strong concerns about any interference in our parliamentary democracy," at a meeting with Chinese Premier Li Qiang at the G20 summit in India on Sunday.
But he faced further demands from lawmakers to toughen his stance on China.
The Chinese embassy in the U.K. said the allegations were made up.
"The so-called claim that China is suspected of 'stealing British intelligence' is completely fabricated and malicious slander," the embassy said on its website.
Britain had been hoping to improve ties with China, with Foreign Minister James Cleverly visiting Beijing last month to make the first tentative steps to repair relations.
But Britain's security services have long warned politicians about the threat posed to parliament.
Last year, MI5 Director General Ken McCallum warned politicians that the Chinese authorities were playing "the long game" in cultivating contacts.
He said they were "seeking to co-opt and influence not just prominent parliamentarians from across the political landscape, but people much earlier in their careers in public life, gradually building a debt of obligation."
But so far, government ministers suggested there would be no change in London's approach, which Sunak sees as engaging with China while being able to raise points of disagreement.
"They do represent an epoch-defining challenge to the UK, (but) we do not think it is right to reduce the approach to just one word," Sunak's spokesperson told reporters when asked whether China should be seen as a threat to Britain.
"We need to take the opportunity to engage with China, not to just shout from the sidelines."
Labour's Starmer said the government should set a clear policy on China.
"The very big question now ... is was this raised when these arrests took place back in March or has it only been raised now that it's come into the public domain?" he told reporters.