A ruling by the UK’s Special Immigration Appeals Commission has revealed that a Chinese businessman with links to King Charles’ younger brother, Prince Andrew, has been banned from Britain. The commission was upholding a decision originally taken in 2023 by the then home secretary, Suella Braverman, to exclude a man subsequently named as Yang Tengbo.

Britain’s Security Service, MI5, had advised the commission that Yang posed “a risk to UK national security”. Reports have noted Yang’s visits to royal events at the request of the prince and his communications with one of Andrew’s senior advisers, Dominic Hampshire.

That Andrew might have been cultivated by an agent of the Chinese government will come as no surprise to anyone who has studied the work of intelligence agencies. Their ideal target will not necessarily be someone who sympathises with the regime they serve. Indeed with the collapse of the ideological certainties of the cold war, this has become increasingly unlikely.

Rather, a target will probably be someone who has particular weaknesses that can be exploited, often revolving around money or sex. They are seldom at the very pinnacle of power. But that, in itself, can leave them resentful and hungry for affirmation.

An exaggerated sense of self-importance can render them even more pliable. This can make for a complex relationship between intelligence predator and their prey.

In Andrew’s case, there are indications that members of his circle actually talked up the prince’s importance as a political contact. The commission’s ruling quoted a message from Hampshire to Yang in March 2020 after the latter had been invited to attend the Prince’s 60th birthday party.

Hampshire told Yang: “I also hope that it is clear to you where you sit with my principal and indeed his family. 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.”

Those more familiar with the workings of the British government might be sceptical about the height of the branches Yang had reached. King Charles is, after all, a constitutional monarch with few formal powers. And Andrew has become an increasingly marginalised figure within the royal family.

A steady stream of revelations about his relationship with sex-trafficker and paedophile Jeffrey Epstein has left him increasingly out in the cold. He was stripped of his role as UK trade envoy in 2011 and was then forced to step down from public duties in 2019. So why bother trying to court him?

Clues are provided in an important survey of the links between the royal family and the intelligence community published by international history specialists Richard Aldrich and Rory Cormac in 2021. As they note, before 2011, Andrew had enjoyed a long career in the royal navy and then as a British trade envoy, becoming closely involved in the sensitive and secretive world of UK arms sales.

In 2010, the Wikileaks revelations suggested Andrew had been fiercely critical of the Serious Fraud Office for almost derailing a deal with Saudi Arabia and that his inside knowledge might have extended to some dark corners of the arms trade and its methods. There were also reports that the UK’s foreign intelligence service, MI6, was concerned that a former US deputy police chief close to the investigation into the Epstein affair might have leaked details to Russia, leaving Andrew open to blackmail.

So Andrew probably was a tempting target, combining personal vulnerability with knowledge that could, at the very least, be embarrassing to the UK. But then, to borrow former US defense secretary Donald Rumsfeld’s vivid phrase about Iraq, the British establishment has long provided foreign intelligence agencies with “a target-rich environment”. And the waters tend to be muddied by the ease with which legitimate contacts based on cultural and trade diplomacy can morph into something more sinister.

The ruling of the Special Immigration Appeals Commission quoted from a statement by the director-general of MI5 from July 2022 which distinguished between legitimate diplomacy and “what we call interference activity – influencing that is clandestine, coercive or corruptive”. Yet, in practice, the distinction is often opaque.

When darker forces are at work, it often only becomes apparent as a result of prolonged surveillance of those involved. And that, in turn, assumes Britain’s spies are actually doing their job. Various bodies have questioned whether they are.

In a July 2020 report, the parliamentary intelligence and security committee criticised the intelligence community for not being more curious about certain aspects of Russian activity. The possibility of Kremlin interference in the 2016 Brexit referendum was a significant concern.

The implication – that intelligence officials had been nervous about getting involved in such a sensitive political issue – was rather borne out by the fate of the committee’s report itself. It was delivered to then prime minister Boris Johnson in October 2019 but was not released to the public until well after his pro-Brexit government had won the general election of December that year.

Nor is the Labour party without questions to answer. At the same time as the Prince Andrew scandal was unfolding, Christine Lee, who donated £584,177 to the office of the Labour MP Barry Gardiner, lost a claim against MI5 which had accused her of engaging in political interference on behalf of China. Gardiner has said in response that none of the donations “according to MI5, came from an illegal source” and that he has “ceased all contact” with Lee following the MI5 warning.

Prince Andrew’s behaviour is part of a wider picture and speaks to the general need for higher standards in British public life. Stricter rules on political donations to prevent foreign interference in British politics are long overdue. And people of political influence, including members of both houses of parliament, should be far more closely scrutinised over their relationships with foreign officials and business people. National security, as the term implies, very much begins at home.