Mr Yang first met the Duke of York in 2014 after being introduced by the prince’s then private secretary, Amanda Thirsk.

He attended a St James’s Palace dinner to celebrate Chinese entrepreneurs in the UK before becoming involved with Pitch@Palace, a project set up by the prince to support entrepreneurs.

Mr Yang is recognised as a key figure in launching its Chinese version – Pitch@Palace China – which also won backing from the Chinese government.

UK authorities discovered a letter from Dominic Hampshire, a senior adviser to Prince Andrew, who said Mr Yang could act on behalf of the prince in engagements with potential investors in China.

Mr Hampshire also told Mr Yang in a letter: “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.”

It is unclear if this was a true assertion put forward by Mr Hampshire, who has not spoken publicly since being named in the ruling.

But the Home Office assessed this as evidence that Mr Yang was in a position to “generate relationships between prominent UK figures and senior Chinese officials” which “could be leveraged for political interference purposes” by Beijing.

Prince Andrew said he “ceased all contact” with Mr Yang after receiving advice from the government, but did not specify when communication stopped. His office said they met “through official channels” and there was “nothing of a sensitive nature ever discussed”.

In another display of the Mr Yang’s friendship with the prince, documents from the court case – disclosed to the media on Friday – show Mr Hampshire privately admitted to the Chinese businessman that the duke’s BBC Newsnight interview addressing his links to sex offender and financier Jeffrey Epstein had been “ill advised”.

Prince Andrew’s aide also thanked Mr Yang for standing by the duke.

The letter written in March 2020 on official Buckingham Palace notepaper added: “Under your guidance, we found a way to get the relevant people unnoticed in and out of the house of Windsor.

“We orchestrated a very powerful verbal message of support to China at a Chinese New Year’s dinner and between the three of us, we have written, amended and then always agreed a number of letters at the highest level possible.”

Mr Yang told the Siac court he never had any private meeting with the duke without his staff present and never had direct access to him by phone or email.