Claims that a Commons researcher spied for China are being investigated further, the Speaker told MPs on Monday.
Sir Lindsay Hoyle emphasised in Parliament that it was an “ongoing sensitive investigation”.
He urged MPs to avoid speculating in the Chamber about the case, which he added an “extreme small number of people” had previously been alerted about on a strictly confidential basis “given the national security of this sensitive matter”.
He stressed that vetting arrangements for Parliament were kept under review to deal with “evolving threats”.
The Speaker’s statement came just hours after the Commons researcher accused of spying for China pleaded his innocence as angry MPs said they were kept in the dark about the case for months.
The man, in his 20s, was arrested in Edinburgh, and another suspect, in his 30s, was detained in Oxfordshire in March, Scotland Yard said. They were bailed until early October. But the researcher said on Monday morning he was “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 man said in a statement released by his lawyers, which did not name him.
“To do what has been claimed against me in extravagant news reporting would be against everything I stand for.”
Rishi Sunak was back in Britain after attending a G20 summit in India, where he confronted Chinese Premier Li Qiang on Sunday over “unacceptable” interference in democracy.
But as Conservative hawks stepped up their demands for the Government to get tough with Beijing, the Prime Minister also said that engagement with the world’s number two economy was better than “shouting from the sidelines”.
A Chinese embassy spokesperson said: “The claim that China is suspected of ‘stealing British intelligence’ is completely fabricated and nothing but malicious slander.
“We firmly oppose it and urge relevant parties in the UK to stop their anti-China political manipulation and stop putting on such self-staged political farce.”
The alleged spy is understood to have had contact with a number of MPs including Tom Tugendhat, before he became security minister, and Alicia Kearns, chair of the Commons foreign affairs committee.
MPs who have been sanctioned by China queried the timeline since the March arrests, which only emerged over the weekend in a spying claims story by The Sunday Times.
“Who knew what, when?” Tory Tim Loughton told Times Radio, asking why the sanctioned MPs were not given a private briefing.
“What discussions have gone on between ministers and Chinese officials to haul them up over this one? Because the prime minister took it up with the premier from China at the G20 summit, as if this is something that had just happened. and it’s not,” Mr Loughton said.
Former Conservative leader Sir Iain Duncan Smith - who hotly criticised a trip to Beijing last month by Foreign Secretary James Cleverly - said it was “time to speak through strength not weakness” in the Government’s dealings with China.
But Business Secretary Kemi Badenoch insisted that Britain was “of course” safe under a Conservative Government, and said she was “extremely confident” about her own staff.