Public bodies in Devon are being charged millions by King Charles and Prince William’s private estates, according to an explosive new expose on the Royal family’s finances.

The investigation by Channel 4’s Dispatches and The Sunday Times revealed that the Duchies of Cornwall and Lancaster reportedly made about £50m in the past year alone from charging rent to the Ministry of Defence (MoD) and the NHS, as well as schools and charities across the country.

The vast business empire includes a portfolio of land, properties and various assets, with the Duchy of Cornwall (DoC) being valued at more than £1bn.

But despite operating as a commercial venture and providing income for both the King and Prince William, the Duchies are run as private estates and are exempt from paying corporation and capital gains tax.

Moreover, as they are separate from the Crown Estate, the chancellor of the exchequer does not receive any of the Duchies’ profits.

There is added controversy as the Crown has refused to reveal details of the properties they own.

However, the C4/Times investigation compiled a dossier of all the DoC’s land registry titles and found that in Devon there is a 25-year leasehold deal with Dartmoor Prison, amounting in total to £37.5m – the equivalent of £1.5m a year – despite the prison being empty.

Earlier this year, all 175 inmates were moved to other jails after high levels of the radioactive gas radon were detected, although all the repairs to the prison are still being funded by the taxpayer.

Nearby, Dartmoor’s Princetown Primary Community School is paying the DoC £15,200 plus VAT in annual rent – amounting to £600,000 during the lifetime of the lease.

In addition, the MoD pays for the British Army to go on training exercises on Dartmoor, where the DoC owns 67,500 acres of land.

In the South Hams, the Royal Navy has paid more than £900,000 over the last 10 years for the right to moor boats near the Britannia Royal Naval College, where Prince William trained as a naval officer, as the DoC owns the bed of the Dart Estuary.

In 2017, the Royal Navy also signed a deal to access its own fuel depot at Devonport, in Plymouth, to refuel warships, including Trident nuclear submarines, for £10,000 a year.

There is also a £3,250-charge to use a jetty, which cost the MoD at least £900,000 to build. The duchy even charges a £100 fee to deploy navigational beacons in Plymouth Sound.

In total, the Royal Navy has been charged more than £1m since 2004 by the DoC to use its jetties.

According to King Charles, the profits are used to fund official and charitable work as well the monarch’s private activities.

But the investigation has also revealed that the Duchies are making money off charities, including ones the King is patron of, such as the RNLI, which is charged £600 rent to put landing slipways on foreshores, including Salcombe.

Devon County Council also pays the DoC £300 a year, amounting to £15,000 over its 50-year lease to use Princetown Fire Station.

The Duchies’ tax exemption status has been widely criticised, with one leading tax advisory firm, Blick Rothenburg, telling The Times that it gives the Royals an “unfair competitive advantage”.

Former home office minister Norman Baker went further. Speaking on LBC, he said the Royal Family was interested in “serving themselves, rather than serving the country”.

He said: “In terms of the naked greed with which the Royal Family tries to exploit every single last penny from the public purse, they are interested in serving themselves, rather than serving the country when it comes to money.

“They are, in my view, public bodies, and they should be transferred to the Crown Estates, and the money should be used to benefit the taxpayer, rather than the taxpayers subsidizing one of the richest families in the country.

“It’s just greed, greed, greed.”

Mr Baker pointed out that the Sovereign Grant - the annual payment the Royal Family receives from the government – was also set to rise to £132m in the next financial year, up from £7.9million in 2011.