Downing Street has denied dragging the King into politics after Sir Keir Starmer joined Charles on a rare joint engagement to see a housing project.
The King took the Prime Minister and Deputy Prime Minister Angela Rayner on a visit to a Cornish development he inspired.
The joint trip came days before Sir Keir is expected to set out further measures as part of a pledge to build 1.5 million homes ahead of the next election.
The King, Sir Keir and Ms Rayner carried out three engagements in Nansledan, a 540-acre extension to the seaside town of Newquay.
The visit is understood to have followed conversations about housing over the past few months between Charles and Sir Keir, during which the Nansledan project was mentioned.
Asked if making the visit ahead of the announcement risked the King being dragged into politics, the Prime Minister’s official spokesman replied: “No.”
He added: “Obviously, this project is entirely run by the Palace and the Duchy (of Cornwall), but the Government has spoken repeatedly on its ambitions on housebuilding, it is a key part of the Plan for Change to deliver 1.5 million homes, to tackle the housing crisis that we’ve inherited, to drive economic growth across the country.”
Sir Keir is said to have expressed an interest in seeing the development in person, with Charles offering to show him around, an invitation accepted by the Prime Minister and his deputy, who is also the Housing Secretary.
Both Charles and Sir Keir share an interest in modern housing developments, with Nansledan and Poundbury in Dorset demonstrating the kind of communities the King believes should be created.
The Prime Minister has set up a taskforce to create the next generation of new towns as part of his housebuilding drive.
He is expected to set out further details of his housebuilding plans later this week and the visit with the King followed the Government announcing measures to streamline the homebuying process.
During the first engagement on Monday, the three “principals” – as they were referred to by staff – visited Newquay Orchard, which employs 45 staff.
They were given a tour by the site’s chief executive Charlotte Hill, and saw the cafe, community kitchen and allotments.
Ms Hill said after the visit: “It is not often that we get this opportunity and it is really good for us to be able to demonstrate just what can be done.”
She told her visitors how the orchard provided services from career guidance to well-being sessions and art events.
At the allotments, they spoke to students and volunteers including Rory Bendle, who had met Charles during a previous visit.
Mr Bendle, 29, said: “I was really surprised to see all three of them.
“I met the King when he was Prince Charles. He is a very calm and gentle person. I told him today that my middle name is also Charles and we had a laugh about that.
“I wasn’t expecting the Prime Minister to come over and talk to me too.
“He asked me about the orchard. I said it was a field and now it has extended to all this, for the community.”
The orchard was designed to help join the Nansledan community to the rest of Newquay, with the Duchy of Cornwall supporting the development of the community building.
Later, Charles returned to Nansledan School, which he had formally opened five years ago, to show the Prime Minister and Deputy Prime Minister around.
During the visit, the visitors met primary school pupils taking a PE class in the sports hall before visiting the science and food tech classrooms.
Students showed the King how they were making vanilla cupcakes and Charles asked about the ingredients they were using.
Referring to the mixture, Charles asked: “At what point is it ready? The problem then is transferring in those (paper cases).
“By the time you get home will you be able to have a few of them and take them with you?”
While the King was speaking with pupils about baking, Sir Keir and Ms Rayner spent time with students in a science class.
The King, Prime Minister and Deputy Prime Minister then walked to the Kew An Lergh development where they met residents, business owners and construction workers building the estate.
Nansledan, which means “broad valley” in Cornish, is a 540-acre extension to the town of Newquay.
When completed, around 3,700 homes will have been built, with the development based on principles of mixed use, mixed income, walkability and sustainability.
Monday’s visit is believed to be the first time in recent history that a monarch has been accompanied by a prime minister and deputy prime minister on a joint royal engagement, focusing on a royal-inspired project.
In 1998, Charles as the Prince of Wales took deputy prime minister John Prescott on a tour of his Poundbury development on Duchy land in Dorchester, Dorset, after personally inviting him to see the housing project.
