The senior Government adviser at the heart of the Chinese spying row was a member of a secretive network used by Beijing to cultivate Britain's elites.
Jonathan Powell, Keir Starmer's national security adviser, was a fellow of the 48 Group, a lobby club founded by British communists which allegedly 'grooms' British politicians and business leaders to fall under the sway of China's Communist Party.
Sources have pointed the finger at Mr Powell for the Government's failure to state that China represented a threat to national security - an omission which the Director of Public Prosecutions has said led to last month's collapse of the trial of Chris Cash and Christopher Berry on charges of passing secrets to China between 2021 and 2023. Both men were formally declared not guilty and deny any wrongdoing.
The Tories have accused ministers of causing the collapse of a major spying trial because they feared that calling China a national security threat might jeopardise trade relations.
The Government has denied interfering with the case.
The 48 Group, which is one of the most prominent pro-China lobbying organisations in Britain, says its aim is to improve trade relations between the two nations - but has been accused of furthering the Beijing regime's wider causes in Britain, as this newspaper first reported in 2020.
Its patrons have included Labour grandee Peter Mandelson, who was recently sacked as Britain's Ambassador to the US over his links to paedophile Jeffrey Epstein.
Both Tony Blair and former Tory Chancellor George Osborne have attended events hosted by the 48 Group in London.
Parliamentary aide Christopher Cash, 30, (pictured) and British teacher Christopher Berry, 33, were each charged with the offence of spying under the Official Secrets Act
Cash and Berry (pictured) were set to face trial this month, but proceedings against them were stopped after the Crown Prosecution Service said it could 'no longer proceed to trial' due to a lack of evidence
Another member of The 48 Group is Yang Tengbo, 50, an alleged Chinese spy who has been accused of developing business relationships with Prince Andrew on behalf of the Communist regime.
Tengbo, 51, was banned from re-entering the UK in December on national security grounds.
Mr Powell is listed as a 'fellow' of the 48 Group on its website.
His elder brother, Lord Powell of Bayswater, 84, a former private secretary to PM Margaret Thatcher, is also listed as a fellow of the group alongside Blair, former Scottish First Minister Alex Salmond, former London mayor Ken Livingstone, former Lib Dem leader Vince Cable and Labour grandee Jack Straw.
Jonathan Powell, 69, was Tony Blair's chief of staff from 1997 to 2007, and joined bankers Morgan Stanley shortly after leaving Downing Street.
Then in 2011 he founded a 'conflict resolution' think-tank called Inter Mediate.
In that role, he has made several trips to China where he held meetings with the Grandview Institution, which has been called a 'front' for China's main foreign intelligence agency, the Ministry of State Security (MSS).
One former diplomat, who does not wish to be named, said: 'I was told before a visit I was going to make to Grandview that it was an MSS cover. I was told that officially.'
Some of Grandview's senior fellows either worked as MSS intelligence chiefs or were in the People's Liberation Army.
Mr Powell attended an event hosted by Grandview entitled US-China Strategic Security and Stability Dialogue in September last year, a month before he was made Sir Keir's national security adviser.
On Saturday, Clive Hamilton, the author of a respected book on China's influence abroad called Hidden Hand, said Mr Powell could be compromised because of his links to both the 48 Group and Grandview.
He said: 'Powell seems to have close links with an organisation in China that is stacked with high-level intelligence officers. Grandview is a nest of spies.
'At best this looks like naivety. For the PM's national security adviser it's beyond belief. My guess is he has no idea who his new friends are. Either he is spying on them or he has been won over to their way of seeing the world.
'Whatever the case, Powell's position has become untenable, especially after [the collapse of the spy case] with the two Christophers.'
On Saturday, The Times reported that Cabinet ministers thought Mr Powell's position was increasingly unsustainable.
One said: 'I am concerned that a narrative builds up that we are not strong enough on China. Our strategic approach [under Powell] is a little bit fuzzy.
'He has become almost like a Cabinet minister in that the focus is on him and his policy positions, which is never really a great situation to be in as a non-elected official.'