Two men have been arrested under the Official Secrets Act amid allegations that a parliamentary researcher spied for China.
The researcher has had links to several senior Tory MPs, including security minister Tom Tugendhat and foreign affairs committee chairwoman Alicia Kearns.
Th Briton was arrested along with another man by officers on March 13 on suspicion of spying for Beijing, it was revealed by the Sunday Times.
Officers from the Metropolitan Police’s Counter Terrorism Command, which oversees espionage-related offences, are investigating.
One of the men, in his 30s, was detained in Oxfordshire on March 13, while the other, in his 20s, was arrested in Edinburgh, Scotland Yard said.
Both were held on suspicion of offences under section one of the Official Secrets Act 1911, which punishes offences that are said to be “prejudicial to the safety or interests of the state”.
“Searches were also carried out at both the residential properties, as well as at a third address in east London,” a statement from the force said.
Both men were held at a south London police station until being bailed until early October.
Mr Tugendhat is said not to have had any contact with the researcher since before he became security minister in September last year.
Ms Kearns declined to comment, adding: “While I recognise the public interest, we all have a duty to ensure any work of the authorities is not jeopardised.”
The Inter-Parliamentary Alliance on China pressure group said it was “appalled at reports of the infiltration of the UK Parliament by someone allegedly acting on behalf of the People’s Republic of China”.
A source close to Ms Kearns told the PA news agency: “It is inevitable the Chinese Communist Party (CCP) would target and seek to undermine Parliament’s leading voices who have demonstrated the ability to constrain the CCP’s ambitions.”
They said that the allegations, if true, would be a “serious escalation and shows the CCP will go to any length to attack thorns in their side”.
The arrests emerged a little over a week after Foreign Secretary James Cleverly visited Beijing amid criticism from some senior Conservatives, who are critics of China.
He insisted the UK would have a “pragmatic” relationship with China to tackle major global issues such as climate change.
Former Tory leader Sir Iain Duncan Smith, one of the party’s most prominent China hawks, warned of a “deepening threat” being posed by the country under President Xi Jinping.
Sir Iain told PA: “This story gives the lie to the Government’s attempt not to see China as a systemic threat.
“Time for us to recognise the deepening threat that the CCP under Xi now pose. What price was Cleverly’s kowtow visit to Beijing?”
A report from Parliament’s spy agency watchdog, the Intelligence and Security Committee, warned in July that Beijing is targeting the UK “prolifically and aggressively”.