The Duke and Duchess of Sussex, who returned to Britain a fortnight ago, are also understood to be concerned that the timing of the King’s announcement may be linked to a crucial meeting on their security arrangements.

Harry and Meghan are still pushing for 24/7 armed police protection now they are back in the UK with their children, Archie and Lilibet, amid concerns about their safety on the school run.

The Royal and VIP Executive Committee (Ravec), the Home Office body responsible for decisions on royal security, is reportedly due to meet as early as today to discuss arrangements for the Sussexes.

But last night the King ruled out any role for Harry and Meghan within the Royal Family in the lead-up to the crunch security meeting.

A spokesman for the Duke and Duchess said: ‘We were a little surprised not to have been told about this in advance.’ The publication of the letter had caught the couple off guard, he said.

Palace sources told the Daily Mail that the release had nothing to do with the security issue or any Ravec meeting. The letter was ‘shared’ with Harry’s team and then released publicly in the interests of ‘transparency’.

The Daily Mail has asked the Duke and Duchess of Sussex to comment.

Publication of the letter came as Prince Harry conducted his first official outing on Monday since arriving back in Britain – and will be seen by many as particularly timely.

He was pictured smiling at the Tower Bridge Studios in London and signing a mural on a wall during a pseudo-royal engagement.

A source told People: ‘He [Harry] was very, very pleasant to everyone. And he was very pleased to sign our celebrity wall. It was all very relaxed.’

King Charles’s letter told more than 100 ‘senior stakeholders’ across the country that his son and daughter-in-law are not working royals with a reminder that their HRH titles remain on ice.

It comes after sources close to the couple repeatedly briefed select media about plans for their new life back in Britain.

They include a resumption of public engagements with the media invited to attend. Some of the couple’s friends have even boasted that Harry has finally secured the ‘half-in, half-out’ deal he always wanted – with the freedom to mine lucrative commercial opportunities while undertaking limited official duties by the ‘back door’.

That model was firmly rejected as unworkable by his grandmother, Queen Elizabeth, at the so-called ‘Sandringham Summit’ of January 2020, which led to the Sussexes’ acrimoniously quitting, not only royal life, but also Britain while embarking on a series of very public attacks on the institution.

Now the King has moved decisively to quash speculation over their return, and publicly re-enforce the boundaries laid down by his late mother.

And he makes clear that Harry and Meghan’s public appearances should not be treated as royal engagements and no public money should be spent on them.

Later, Meghan’s As Ever Instagram page posted a photo of the Duchess petting a dog in the sunshine in what is thought to be the first picture of her put online since the Sussexes arrived back to the UK.

The letter released on Monday was written on His Majesty’s instruction by his Lord Chamberlain, Lord Benyon, head of the Royal Household, following ‘a number of requests for guidance’.

It states clearly that ‘there is no change to the current status of the Duke and Duchess of Sussex. Their styles as His and Her Royal Highness remain in abeyance and are not used.’

It adds: ‘The charitable work of the Duke and Duchess is a personal matter for them both and undertaken in their private capacity. In short, their position is akin to private citizens with commercial and charitable interests.’

Harry and Meghan have said they were ‘surprised’ by the King’s bombshell letter making it crystal clear they will be treated as ‘private citizens’ rather than working royals

Meghan’s As Ever Instagram page posted the first picture of the Duchess since she returned to the UK today. It showed Meghan playing with a dog in the sunshine

Former press secretary to Queen Elizabeth, Ailsa Anderson-Cole, told the Daily Mail that the letter was ‘decisive and unequivocal’.

‘It was also cleverly done, making their position clear, but in response to queries by stakeholders [rather than by issuing their own statement].’ she said.

‘The King is taking charge of the narrative and acting decisively to end any speculation.’

The letter was sent to the duke and duchess’s team shortly before it was made public, without any discussion over its contents, the Mail understands.

Among the ‘senior stakeholders’ to receive it were the 98 Lord Lieutenants who are the monarch’s representatives in counties across the UK.

The Daily Mail understands that Buckingham Palace had been contacted by a number of officials seeking clarity about operational matters pertaining to the Sussex family while they are resident in the UK.

Officials stressed that there was nothing new in its contents, and that it simply reiterated Buckingham Palace’s position ‘in full accordance with the Sussex family’s stated wishes to remain private citizens while in the UK’.

It was, they added, ‘in keeping’ with the Sandringham agreement, which still very much stands. However, the fact that the Palace chose to send the letter out demonstrates the level of consternation and confusion sparked by the family’s sudden return.

The suggestion that the guidance has been issued to make clear the ‘continued position for the benefit of all parties’ will be interpreted by some as a warning shot across the Sussexes’ bow.

‘People have been asking for clarity. The guidance is both consistent and clear,’ a source told the Daily Mail.

The letter is also at pains to stress, given Harry’s continued lobbying of the Home Office to reinstate his taxpayer-funded police protection now he has returned home, that this remains a matter for the department’s executive committee Ravec to determine, and not the King.

It is expected to make a ruling on the matter in the coming weeks. In the meantime, the palace says questions over security around a visit by Harry or Meghan should be referred to the local police authority.

Since their decision to quit the UK in 2020 and his loss in the High Court against the Home Office security decision, Harry maintained it was unsafe for him to bring his family to the UK.

Just a year ago he publicly stated that he could not foresee a time this would ever happen.

But in July he brought Meghan and their children, Prince Archie, seven, and Princess Lilibet, five, over for a short holiday during which they met King Charles at Highgrove for the first time in four years.

Then last month sources close to the prince revealed they had suddenly decided to return to the UK. The King was only told of the move four days before the news was made public and the family arrived just two weeks later. It is understood they have settled in the Cotswolds, with the children enrolled in a local private school.