MI5 built a case against an alleged Chinese spy who befriended Prince Andrew after a Mail on Sunday exposé, newly released documents reveal.

An exclusive investigation by this newspaper in 2020 detailed how a lobbying firm set up by Yang Tengbo had gained access to key establishment figures, including the Duke of York.

We revealed how Yang, 50, was a former Chinese government official whose firm, Hampton Group, secured links to Andrew’s organisation Pitch@Palace.

The suspected spook would later be stopped by police at Heathrow airport and have his mobile phone, laptop and iPad seized. He was banned from the UK on national security grounds.

Now, a cache of court papers, released last Friday, reveal how he appealed to the Investigatory Powers Commissioner (IPCO) in a bid to force MI5 and the police to destroy a series of bombshell documents they had downloaded from his electronic devices.

It led to the UK authorities disclosing to him the ‘open source’ material they had gathered – including our story, which they then used to justify the retention of his data.

In one document, Yang accused the Home Office of relying on this newspaper’s reporting about him and argued he should be granted anonymity. 

He said: ‘I know that the Home Office is prepared to rely on media stories in relation to its claims about me. Further reporting of this nature would be very harmful to, among other matters, my business interests and the Hampton Group.’

 In another document, Yang’s lawyer claimed Buckingham Palace knew about his association with Pitch@Palace.

Yang lost his bid to force the Government to destroy his files but he was granted anonymity and was known only as ‘H6’ until reporting restrictions were lifted in December.

Other court documents revealed extraordinary details of the Duke of York’s connections with Yang.

One document found on Yang’s phone claimed Andrew planned to raise $3 billion for an initiative called the Eurasia Fund. Yang was authorised to act on behalf of the duke in talking to potential Chinese investors for the fund.

He said last week the allegations were unfounded, adding: ‘I have done nothing wrong.’