Some will see it as an act of kingly statecraft, a timely shot across their quasi-royal bows. To others it is a vital sign that Prince Harry’s and Meghan’s presence in Britain will not be allowed to destabilise the monarchy.

What is unquestionably clear, however, is that less than two weeks after their return to British shores, one thing remains unchanged: Megxit still means Megxit.

The decisive move by the King – strongly supported, I am told, by Prince William – means that just because the couple are home there will be no softening of attitudes nor any dilution of the uncompromising view of the late Queen Elizabeth that they could never be ‘half-in, half-out’ royals.

That the unprecedented announcement should come on the eve of the fourth anniversary of the Queen’s death will be lost on no one, including her grandson, Harry.

This official affirmation of his and Meghan’s continued status as non-working royals is the first since their bitter departure more than six years ago.

It is also timely, with a flurry of key royal events imminent, including Prince George’s first day at Eton College.

The letter, issued in the name of the Lord Chamberlain, Lord Benyon, the King’s most senior aide, is a rigid reminder that the Duke and Duchess of Sussex are to be treated as ‘private citizens’ while in Britain, and do not represent the Royal Family.

Nor can they use their HRH titles which, Lord Benyon emphasises, ‘remain in abeyance’.

Should there be any lingering doubts among Sussex supporters – or indeed the couple themselves – that returning to the UK might lead to a more flexible approach, with the couple wanting to ramp up their charity work, such hopes look wildly misplaced.

The Lord Chamberlain may have drafted the official communique, which has been sent to members of the Government, the military and Lord Lieutenants, but the content is very much in line with Charles’s sentiments.

In practical terms, it was designed to make clear to those who are involved with royal visits that any engagements carried out by the Sussexes will be in a private capacity.

And it shows that the outcome of the so-called Sandringham Summit in 2020, which led to their departure, still stands.

The language and the icily formal tone of the draft are striking. Stressing that the purpose of the letter was to ‘avoid doubt or confusion’, it says the couple do not represent the sovereign.

While any charity work they do ‘is a personal matter for them both and undertaken in their private capacity’.

One passage gives the most distinct view of how this once-golden couple are viewed. ‘In short,’ the letter says, ‘their position is akin to private citizens with commercial and charitable interests.’

Reading between the lines, the only way to divine the directive on how they are to be treated is as a command.

Royal aides may insist that there is nothing controversial, nor new, about the letter’s contents adding that it merely sets out the position for all parties.

But the fact that Buckingham Palace needed to send the letter in the first place illustrates the degree of confusion and uncertainty Harry and Meghan’s sudden return to the UK has caused.

As one long-term friend of the King told me: ‘They didn’t need to issue guidance about Andrew Mountbatten-Windsor when he ceased his royal life and gave up public duties, which suggests they have been spooked by the Sussexes.’

One factor that has raised concern at the highest levels, has been the way friends of Harry and Meghan have been spoon-feeding friendly publications with details about their plans. ‘They’ve only been back a matter of days and can have barely unpacked but we keep hearing how they want to step up their charity work which would inevitably raise their public profile,’ says one figure. ‘It’s exasperating.’

Talk, too, of the couple establishing some kind of rival court has also irritated figures close to the King.

The Lord Chamberlain’s letter, which he says was a response to ‘a number of requests for guidance’, should indeed be viewed therefore as a shot across the Sussex bows – or at least across the bows of those pushing their agenda.

The problem, however, is that it is all very well telling organisations that any visits Harry and Meghan undertake should not be treated as royal engagements, but in the years since they left Britain that is precisely the way their appearances have been treated. Even their visits overseas have been crafted to resemble the kind of duties they carried out before they abandoned their royal life, often with the same protocols, such as paying respects in war cemeteries.

As Harry himself has often chosen to remind people – not least in his battle to obtain taxpayer-funded security – he has always been a royal.

Yesterday’s intervention will be seen as an essential move by the King to preserve the cohesion of an institution which was undermined in the first place by the Sussexes flouncing off to California.

And while it may not prevent the couple seeking out public-facing opportunities, it may change the way people react to them.

Of course, the letter leaves many questions unanswered. It does not address the issue of family events and when and where Harry, Meghan and their children might join private House of Windsor gatherings.

Nor does it offer any insight into the police protection Harry so passionately wants, with his children about to start at school and the potential risks of shuttling them to and from the same place each day.

Aware that such concerns may be raised, the Lord Chamberlain dodges it, writing: ‘Any operational security issues should continue to be directed to the relevant police authorities.’

However, he does acknowledge that accommodating the couple may be contentious and suggests that any questions ‘where recourse to public funds may be required, should be directed to Buckingham Palace’.

A sign, perhaps, that the King will intervene if he does feel Harry and Meghan’s conduct may not be in the monarchy’s best interests.

Many critics believe that although the letter was designed to draw a line under speculation about the couple’s future, there was a missed opportunity. ‘Removing them from the royal website [where they still feature but without their HRH titles] would have been the most significant gesture to separate them as non-working royals from the rest of the family,’ a former aide to the King said.

After their tours of Africa, Central America and Australia, where they were treated as huge royal stars, it might have been useful if the Lord Chamberlain had also sent a copy of his letter to world leaders too.