Dominic Hampshire played a key role in the development of Yang Tengbo’s relationship with the Duke of York – but the full details of what happened between the three men remain unclear.

Last month a court rejected Mr Yang’s appeal against being banned from the UK, after an intelligence assessment that he could be secretly working for the Chinese state. Mr Yang has denied all wrongdoing.

Lawyers for the BBC and other media organisations argued at the Special Immigrations Appeal Commission (Siac) on Friday that Mr Hampshire could not keep his account private simply because he had lacked the “common sense” to find out if it might become public.

In December, the court said Mr Yang had formed an “unusual degree of trust” with the prince and had not disclosed his links to an arm of the Chinese Communist Party clandestinely involved in political interference.

It upheld the home secretary’s conclusion that he was a threat to national security.

The BBC and other news organisations are now asking Siac to release a witness statement that Mr Hampshire wrote in support of Mr Yang after the aide had been first contacted by British intelligence.

In submissions on Friday, lawyers for Mr Hampshire said that he had sought assurances from Mr Yang’s lawyers that the witness statement would remain private – and he had only realised it could become public when he arrived at the appeal hearing last July.

Mr Hampshire then withdrew the statement in an attempt to prevent it from becoming public.

“I was told that the information [in the statement] would be kept private and confidential,” Mr Hampshire said to the court in written submissions on Friday.

“If there was any question of this being available in the public domain, I was not warned of it.

“If I had been, I would never have agreed to submit a witness statement, much less go into the level of confidential detail which I did.

“I wrote what I did in the statement with such candour – including about my own confidential commercial interests but also about the private interests of third parties – in the expectation it was for the private attention of one of the most senior ministries of state on a grave matter.

“I quite simply would not have volunteered to write about those matters had I known that there was any chance, however small, that it was for use in a forum which was or could become public.”

Adam Wolanski KC, representing the media organisations, said there was an exceptionally strong public interest case to release Mr Hampshire’s account to journalists, along with other documents that remain confidential.

“It is extraordinary that a person in Mr Hampshire’s position, apparently charged with dealing with confidential and sensitive matters on behalf of the Duke of York, did not bother obtaining his own legal advice before agreeing to provide a witness statement to Mr Yang,” said Mr Wolanski in written submissions.

“Mr Hampshire cannot now pray in aid his mystifying and unexplained decision to give a witness statement in this obviously highly contentious matter without seeking his own legal advice.

“He should not be permitted to benefit from his, to put it kindly, lack of common sense and his bad decision to proceed without legal advice.

“The court must instead proceed on the basis that he made this decision with his eyes open, knowing the risk that the evidence may become public.”

Mr Yang became a highly trusted confidante of Prince Andrew following the duke’s interview with the BBC’s Newsnight programme in November 2019, which detailed the Duke’s friendship with sex offender Jeffrey Epstein.

The fallout from the interview led to the prince withdrawing from public duties – and the end of his commercially successful Dragons Den-style investor events in the UK and China.

In March 2020, Mr Hampshire told Mr Yang in a letter that he had managed to salvage the prince’s reputation in China.

Seven months later the businessman was authorised to represent the prince in China in a planned $3bn investment fund.

The “Eurasia Fund” scheme aimed to raise cash to invest in Chinese state projects in Africa and the Middle East.

Developing the regions is a cornerstone of the Chinese Communist Party’s plan to expand its diplomatic and financial reach.

The discovery of the scheme, and the fear that the prince was being drawn into a complex Beijing plan to influence him, led the home secretary to ban Mr Yang from the UK.

He has denied all wrongdoing – saying he is a legitimate businessman who has worked for decades to improve links between China and the UK.

Mr Yang came to study in the UK in 2002 and later set up a series of China-related travel and business consultancy firms.

He met the Duke of York in 2014 and later took on a role in the China-based version of Prince Andrew’s “Pitch@Palace” events, in which entrepreneurs sell their ideas to investors.

Siac will rule later on whether further documents from the case will be made public.

In a statement, his office said Prince Andrew had met the man “through official channels” and there was “nothing of a sensitive nature ever discussed”.

The alleged spy has been banned from the UK following a judgement by the UK’s semi-secret national security court.

The man, known only as H6, was described in court as a “close confidant” of Prince Andrew who had formed an “unusual degree of trust” with the duke.

In 2023, H6 brought an appeal against his initial ban but the decision has been upheld by the court.

Judges were told the businessman was attempting to leverage Prince Andrew’s influence.

The duke’s office said he was “unable to comment further on matters relating to national security”.

His statement did not specify when he ceased contact with the man nor the duration of their communications.

Buckingham Palace declined to comment, saying they do not act for the prince, who is not a working royal.

China’s embassy in the UK has denied the espionage claim saying “some individuals in the UK are always eager to fabricate baseless ‘spy’ stories targeting China”.

“Their purpose is to smear China and disrupt normal exchanges between Chinese and British personnel,” a spokesperson for the embassy said.

The former home secretary Suella Braverman banned H6 from the UK in March 2023.He then brought his case to the Special Immigration Appeals Commission, a court set up to consider appeals against decisions to ban or remove someone from the country on national security or related grounds.

In the published ruling, the judges upheld Braverman’s decision.

The court was told that H6 was invited to Prince Andrew’s birthday party in 2020 and was told he could act on his behalf when dealing with potential investors in China.

It is not clear how H6 became close to the prince, but in November 2021 police officers stopped and questioned him at the UK border under powers to investigate suspicions of “hostile activity” by a foreign state.

During that stop H6 surrendered a number of electronic devices including a mobile phone.

What officers found on them so concerned the security service MI5, that Braverman used her exceptional powers to ban H6 from the country.

In a letter found on one of his devices, H6 was told by Dominic Hampshire, an adviser to Prince Andrew: “Outside of [the prince’s] closest internal confidants, you sit at the very top of a tree that many, many people would like to be on.”

Mr Hampshire adds: “Under your guidance, we found a way to get the relevant people unnoticed in and out of the house in Windsor.”

No further details about who the “relevant people” were are given in the excerpt from the letter included in the ruling.

Mr Hampshire also confirmed to H6 that he could act for Prince Andrew in talks “with potential partners and investors in China”.

A document listing “main talking points” for a call with Prince Andrew was also found.It states: “IMPORTANT: Manage expectations. Really important to not set ‘too high’ expectations – he is in a desperate situation and will grab onto anything.”

The court assessed that this meant H6 was in a position “to generate relationships between senior Chinese officials and prominent UK figures which could be leveraged for political interference purposes by the Chinese State”.

The judges said H6 had won an “unusual degree of trust from a senior member of the Royal Family who was prepared to enter into business activities with him”.

They added that the relationship had developed at a time when the prince was “under considerable pressure” which “could make him vulnerable to the misuse of that sort of influence”.

The prince faced increasing scrutiny from late 2019 over his friendship with the late US financier and sex offender Jeffrey Epstein, which included his infamous Newsnight interview in November of that year.

He stepped back from royal duties in November 2019 and the prince has since been dogged by questions about his judgement and his finances.

Questions were raised about the prince’s finances after he reached a settlement – believed to run into the millions – in a civil sexual assault case brought against him by Virginia Giuffre, one of Epstein’s accusers. The prince has always denied assaulting Ms Giuffre.

Isabel Hilton, editor at China Dialogue, told BBC News that Chinese state agents would typically look to target “members of the House of Lords or prominent business people, or people who have a voice in the community”.

She added that it was “quite ambitious” to target a royal and “quite unwise for a member of the Royal Family to allow himself to be targeted”.

Security chiefs feared Beijing was attempting to run an “elite capture” operation to influence the Duke of York because of the pressure he was under, a tactic which aims to appoint high profile individuals to Chinese businesses, think tanks or universities.

H6 was subsequently informed that he was believed by UK authorities to be associated with the United Front Work Department (UFWD), an arm of the Chinese Communist Party (CCP) tasked with conducting influence operations.

The ruling said MI5 Director General Ken McCallum had expressed concern about the threat posed to the UK by political interference by China and that bodies such as the UFWD were “mounting patient, well-funded, deceptive campaigns to buy and exert influence”.

The Home Office said they believed H6 had been engaged in covert and deceptive activity on behalf of the CCP and that his relationship with Prince Andrew could be used for political interference.