Two men have been arrested in the UK under the Official Secrets Act amid reports that a parliamentary researcher spied for China, Report informs via Sky News.
The researcher has links to several senior Tory MPs and has been arrested on suspicion of spying for China, according to The Sunday Times.
He was arrested along with another man by officers on 13 March, the newspaper reported.
The researcher, who is in his 20s, is understood to have had links to security minister Tom Tugendhat, foreign affairs committee chairwoman Alicia Kearns and other senior Tory MPs.
The MPs he is linked to are privy to classified or highly sensitive information.
A senior Whitehall source told The Sunday Times: "This is a major escalation by China. We have never seen anything like this before."
Officers from the Metropolitan Police's Counter Terrorism Command, which oversees espionage-related offences, are investigating.
One of the men, in his 30s, was arrested in Oxfordshire on 13 March, while the other, in his 20s, was arrested in Edinburgh, Scotland Yard said.
"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.
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".
In July, the Intelligence and Security Committee (ISC) said China targets the UK "prolifically and aggressively" in a way that poses a "challenge" for British intelligence agencies.