Former Tory leader Sir Iain Duncan Smith is applying for an urgent question in the Commons on the influence of Beijing’s shadowy United Front Work Department, the group said to be associated with the unnamed man.

Meanwhile, Nigel Farage has said his Reform UK party is prepared to use parliamentary privilege to name the alleged agent, known only as H6, in the chamber unless the courts lift an anonymity order which protects his identity.

Home Secretary Yvette Cooper said Britain has a “complex” relationship with China which requires economic cooperation with the country while also challenging any risk to national security, as she was questioned about the case on Sunday. But parliamentarians have expressed concern about the level of access allegedly gained by the Chinese businessman, who reports suggest also met former prime ministers Lord David Cameron and Baroness Theresa May.

The suspect is said to have become a “close” confidant of the Duke of York, with whom he was described in court as having formed an “unusual degree of trust.” He was first excluded from Britain by then-home secretary Suella Braverman in 2023, when the Home Office said he was believed to have carried out “covert and deceptive activity” for the Chinese Communist Party.

Judges at a specialist tribunal in London on Thursday ruled Ms Braverman had been “entitled to conclude” that he “represented a risk to the national security” after he launched an appeal against the decision. Asked what her message to Beijing would be, Ms Cooper told the BBC on Sunday the Government would “continue to take a very strong approach to our national security”, including towards any challenge from China.

“Of course, with China we also need to make sure we have that economic interaction, economic co-operation in place as well. So it’s a complex arrangement,” she told the broadcaster in an interview.

Shadow home secretary Chris Philp told LBC he was “extremely worried” about the case and that the court order protecting the man’s identity should be lifted so that “justice can be seen to be done”.

The businessman had brought a case to the Special Immigration Appeals Commission (SIAC) after his initial exclusion in 2023 but his appeal was dismissed on Thursday. At a hearing in July, the tribunal was told that an adviser to Andrew said he could act on the duke’s behalf when dealing with potential investors in China, and that H6 had been invited to the duke’s birthday party in 2020.

A letter referencing the event from the aide, Dominic Hampshire, was discovered on H6’s devices when he was stopped at a port in November 2021. The letter also said: “You should never underestimate the strength of that relationship… Outside of his closest internal confidants, you sit at the very top of a tree that many, many people would like to be on.”

H6 was later informed that he was believed by the UK authorities to be connected to the United Front Work Department – an arm of the Chinese Communist Party tasked with conducting influence campaigns.

Sir Iain said he will seek to raise an urgent question “on the infiltration of Government and the political establishment by the Chinese United Front Work Department”. He told the Guardian he would seek to pressure the Government over the foreign influence registration scheme (FIRS), which is designed to protect Britain from covert influence but has not yet been been implemented.

FIRS would require individuals to disclose who they are in an arrangement with, what activity they have been directed to undertake, and when the arrangement was made.

“We want to know: what’s happening to the risk register? Are you planning to continue with it? And are you going to put China in the upper tier?” Sir Iain said.

On Friday, a statement from the duke’s office said: “The Duke of York followed advice from His Majesty’s Government and ceased all contact with the individual after concerns were raised. “The duke met the individual through official channels with nothing of a sensitive nature ever discussed. “He is unable to comment further on matters relating to national security.”