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Why precisely are Meghan and Harry returning to Britain? Through their representatives, they have let it be known that their sudden and dramatic move has been 'driven by the couple's desire to spend time in Europe, [to be] nearer Harry's family and wanting to educate their children in the UK'.

That may be so. But – to use the jargon of the immigration system – could there have been 'push' factors as well as the 'pull' ones they describe?

In other words, could Meghan and Harry be running away from something, just as much as they are running towards something else?

Specifically, huge and pertinent questions remain surrounding Harry's US visa, the document that has until now entitled him to reside there. It is worth stressing that his marriage to a US citizen does not automatically grant Harry the right to live, let alone work, in America.

In 2023, the Heritage Foundation, of which I am a director, sued both the United States Department of Homeland Security (DHS) and the State Department for the release of the Duke's immigration records, in what has become the most high-profile immigration-related case in decades.

Anyone applying to live and work in America has to respond truthfully to the question: 'Have you ever violated, or engaged in a conspiracy to violate, any law relating to controlled substances?'

I regularly answered it myself until I became a US citizen more than a decade ago.

It is unknown how Harry answered the question, assuming it was put to him. But we know his truthful response, whatever he wrote on his form.

It is not known how Harry, pictured here in 2006, answered questions surrounding his past drug use for his US visa

In his highly destructive and unpleasant memoir Spare, Harry boasted in extensive detail of having ingested a bizarre range of illegal drugs, from cocaine and psychedelic mushrooms to the dissociative veterinary anaesthetic ketamine and, predictably, cannabis.

Needless to say, this is a pattern of criminality that would normally bar someone from entering the United States at all, let alone living there.

It is frankly extraordinary that Harry was so brazenly stupid as to have published and promoted a book detailing his enthusiasm for banned narcotics while seeking to live in the US as a foreign alien.

Spare not only displayed deep-seated scorn for Harry's own family, including his father the King and his brother the Prince of Wales. It also made a series of admissions of law-breaking on British soil.

Harry and Meghan's sudden decision to abandon any further attempts at making a success of themselves in America and to scuttle back across the Atlantic to try to regain the affection of the British people does not halt my Foundation's ongoing legal action. Far from it.

In fact the latest developments will only lead to calls for even greater scrutiny of Harry's US visa application by the American people and members of Congress. We remain determined to see Harry's immigration records released in a spirit of openness, transparency and accountability. That is the American way.

The stakes are incredibly high for the Duke, who has admitted that his drug use lasted until at least 2020.

If any wrongdoing by Harry is revealed in relation to his visa application, that would under normal circumstances prevent him from returning to America for the rest of his life.

In his highly destructive and unpleasant memoir Spare, Harry boasted in extensive detail of having ingested a bizarre range of illegal drugs

It is important to mention that the Duke's team has always insisted that he told the truth. However, the point is that until his application is disclosed, the American public won't know the full picture, whatever it might be. This is about transparency.

If Harry were found to have committed an immigration offence while on US soil, he could face up to five years in federal prison, followed by summary deportation.

As a direct result of our Freedom of Information case, the US State Department is reviewing no fewer than 289 documents relating to Harry's visa application, running to almost 2,500 pages. (Some initial documents have been withheld.)

I have separately urged Secretary of State Marco Rubio and President Donald Trump to release these documents to the American people.

No one in America should escape legal scrutiny, including – or perhaps especially, given the republic's foundational history – foreign royals.

Daily Mail readers will be well aware that President Trump has made immigration enforcement and border security a top priority. In fact no US administration in modern times has done more to take decisive action to defend America's borders and restore the country's sovereignty than the present one.

If Harry has nothing to hide about the information he supplied on his US immigration application – and if he answered any questions about his prior enthusiasm for illegal drugs truthfully – he should support the application's release, as well as that of all documents relating to it. I regard his failure to have done so as an insult.

What's more, the Sussexes – and this is particularly outrageous given the inherently apolitical nature of the British monarchy – have never hidden their Left-wing leanings in general and their sympathy for the Democratic Party in particular.

If any wrongdoing by Harry is revealed in relation to his visa application, that would under normal circumstances prevent him from returning to America for the rest of his life

Even their favoured amanuensis, the celebrity tittle-tattle magazine People, admitted recently that 'they have made no secret of their disillusionment with the current White House'; while Katie Miller, the wife of White House deputy chief of staff Stephen Miller, has said: 'They are moving back to Britain because they don't like President Trump.'

Last February, the President himself was asked whether he would deport Harry over the Prince's extensive drug use. Trump replied: 'I don't want to do that. I'll leave him alone. He's got enough problems with his wife: She's terrible.'

Earlier this year, Trump exclaimed to the Daily Mail's Robert Hardman: 'Boy, what she's done to that guy!'

And it is certainly striking just how sudden his and Meghan Markle's decision to flee America has been.

Even the King was allegedly unaware of his son's plans until just a few days ago, while William was blindsided and is said to be furious.

The move is all the more surprising given that Harry and Meghan have spent years relentlessly attacking the Crown, in print and on television, as an unwelcoming and racist institution, while simultaneously moaning about the British media, castigating various members of the Royal Family and complaining about much else in the UK.

Meghan in particular mocked the way she had to curtsey to the beloved late Queen Elizabeth. The Duchess seems to have no fondness whatsoever for the rainy North Atlantic island she quit very quickly after she had found her second husband there.

We deserve to know the truth. We have the right to know whether or not a senior British royal included false information on his immigration documents, whether he received some kind of special treatment, and whether or not his unlikely return to his ancestral country is related to the information he supplied on his visa application.

And I firmly believe that, before long, we will all know the truth.

• Nile Gardiner is a former aide to Margaret Thatcher, and Director of The Margaret Thatcher Center for Freedom at The Heritage Foundation in Washington DC.