The Prince of Wales’s Duchy has been accused of allowing homes on royal land to grow mouldy, according to a new investigation.

People living in rented homes on land owned by the Duchy of Cornwall have claimed there is a lack of insulation and black mould growing in some instances.

The Duchy of Cornwall estate is owned by Prince William after it was passed down from his father the King upon his ascension to the throne in 2022.

The business empire the heir to the throne inherited has more than 600 rental properties and generated profits of £23.6 million in the last financial year. William is understood to pay income tax on the full amount.

The surplus is used to fund the private lives of the Prince and Princess of Wales and their children as well as their official and charitable work.

In a 15-month Channel 4 (C4) Dispatches investigation with the Mirror newspaper, rentals on the royal land have complained about instances of mould and damp.

Some also complained about the lack of eco-upgrades to their homes and the investigation claims to have found that a number of the properties being rented out failed to comply with minimum energy efficiency requirements for landlords.

They found that one in seven of the 500 Duchy residential rental properties they identified have low Energy Performance Certificate ratings.

‘Miserably cold’

The Duchy was established in 1337 and many of the buildings in the property portfolio are more than 100 years old.

The Telegraph understands that the Duchy is committed to continuous improvement of its properties and works closely with its tenants to actively address energy efficiency of properties across the portfolio.

One tenant told the C4 Dispatches programme: “It gets miserably cold in winter, I can only heat two rooms in my home. The Duchy does not understand.”

Another said: “The house is cold, and it is a struggle but there is nowhere else to live here… When the wind blows the curtains start swinging. There’s no heating upstairs at all.”

Claire Williams, 53, allowed The Mirror to take pictures of her former home in the Duchy. The newspaper reported that she was evicted last week over rent arrears, which she disputes.

The former farmhouse tenant in Exeter, who lived there for more than 20 years, said that black mould started growing below ground level many years ago.

“I’ve complained about it for 21 years,” she said, adding: “The repaint was done about a week before I moved in so you couldn’t see it.”

The programme also conducted a five-month investigation alongside The Sunday Times to assess the thousands of properties and their business contracts owned by the Duchies of Lancaster and Cornwall – the King and William’s private estates.

Last year, the Duchy of Lancaster raised £27.4 million for the King while William’s Duchy of Cornwall raised £23.6 million.

The investigation found that the Duchies make millions each year through rents charging councils, government departments, businesses and even the Ministry of Defence.

For example, William’s Duchy was found to have signed a £37 million deal to lease Dartmoor Prison to the Ministry of Justice, charged the navy more than £1 million to build and use jetties and moor warships on its land and charged the Army to train on Dartmoor.

The Telegraph understands that the Duchy rents are set by reference to comparable market evidence and tenants are able to obtain external advice before reaching an agreement.

The Duchy also has a long-standing relationship with the Army, which includes the MoD using the Dartmoor land for training purposes under licensing agreements that date back to the 1800s.

The Telegraph understands that Ms Williams has been in arrears since 2005 and that the Duchy worked closely with her to develop a repayment plan, which she did not follow.

An independent surveyor is understood to have visited the residence in May this year, and found that it had not been heated or ventilated properly and was therefore causing mould. The former tenant is said to have not formally reported damage to the property and has not allowed access for contractors on numerous occasions.

‘Expansive transformation’

A Duchy spokesman said: “The Duchy of Cornwall is a private estate with a commercial imperative which we achieve alongside our commitment to restoring the natural environment and generating positive social impact for our communities.

“Prince William became Duke of Cornwall in September 2022 and since then has committed to an expansive transformation of the Duchy.

“This includes a significant investment to make the estate net-zero by the end of 2032, as well as establishing targeted mental health support for our tenants and working with local partners to help tackle homelessness in Cornwall.”

Elon Musk’s plan to slash American state spending by around $2 trillion (£1.54 trillion) should be taken “seriously”, Boris Johnson has said.

Donald Trump has said he would hire the tech billionaire to lead an efficiency task force if he wins Tuesday’s US presidential election.

At a Trump rally in Madison Square Garden last week, Mr Musk told activists “all government spending is taxation” as he promised a bonfire of government waste.

“You think we can rip off this wasted $6.5 trillion Biden budget? Well, I think we can do at least $2 trillion – yeah, yes, two trillion,” Mr Musk said.

In an interview with CNN on Sunday night, Mr Johnson – who has backed Mr Trump to return to the White House – said there was merit to the saving proposals.

The former prime minister said: “I gather that Elon Musk is going to come in and cut two trillion off government spending.

“So if that’s the agenda, then I think that needs to be looked at seriously. Because I do think there is a case that [in] Western democracies like the UK, perhaps like the US as well, that the state has got too big.”

Mr Johnson had a good relationship with Mr Trump and backed his re-election campaign in January, claiming the “global wokerati” was “trembling violently” at the thought of his return.

According to his former communications director, Mr Johnson feared Britain had been left infantilised by the pandemic response and left in a “permanent state of doublethink”.

Guto Harri told a hearing of the Covid inquiry last year that the former prime minister believed the British state had become “too big, too fat and too expensive”.

During his time in Downing Street, Mr Johnson unveiled a series of tax rises that took the tax burden to what was a record high at the time.

He and Rishi Sunak, his then chancellor, argued that tax rises including an increase in National Insurance were needed in the wake of Covid, the energy crisis and war in Ukraine.

Elsewhere in his CNN interview, Mr Johnson said he “worries a great deal” about the outcome of Russia’s war in Ukraine.

“I do worry a great deal about what will happen in Ukraine and I think it’s the single most important issue that we face in our generation, in the early part of the 21st century.

“And this is the deciding conflict, in my view. It will set the pattern for what happens to decades to come.”

Insisting that current support from the West for Ukraine was not enough “even if Kamala wins”, Mr Johnson also downplayed fears about Mr Trump pulling support for Kyiv.

“Clearly a lot of people worry about that… But I have to speak as I found and when I was foreign secretary, when I had to deal with Donald Trump I have to tell you on a lot of the key issues he was very, very solid,” he said.

“When it came to Iran, when it came to Syria and indeed when it came to Russia and Ukraine, he gave Ukraine those anti-tank missiles when frankly the previous Democrat administration – when you look at how it responded to Ukraine’s invasion – did virtually nothing.”

Mr Johnson added he did not believe he could be “useful” to British politics at the moment after his full-throated declaration of support for new Tory leader Kemi Badenoch.

“I think I was useful in 2019 because we couldn’t get Brexit done. I can’t see at the moment how I can really do anything similar,” he said.

“But I want to be, of course I want to be supportive of my party and of course I’m going to do that.”

Mr Johnson said on Saturday that Mrs Badenoch, who served as his equalities minister until her resignation over the Chris Pincher affair, will bring the Tories “much-needed zing and zap”.