The rent charged to the NHS for the 27,000 sq ft unit near Tower Bridge is 67 per cent more than the Metropolitan Police was paying for the same property months earlier.
The King, who counts the Duke of Lancaster among his royal titles, will earn £11.4 million from the deal by the time the contract expires in 2038.
It comes despite the Duchy of Lancaster claiming it “is completely self-financing and does not rely on any taxpayers’ money”.
The Royal family has three main sources of income: the Sovereign Grant paid out from the Crown Estate, the Duchy of Lancaster, and the Duchy of Cornwall, which has a property portfolio belonging to the Prince of Wales that spans thousands of acres.
The royal addresses, which cover around 180,000 acres of England and Wales, are largely made up of land seized by medieval monarchs.
The two duchies hold more than 5,400 leases between them, which reportedly generate £50 million each year for King Charles and Prince William. This is in part because the domains benefit from special tax status, meaning they pay no capital gains tax or corporation tax on their profits.
Tax arrangements
It has raised fresh questions over the Royal family’s tax arrangements.
The Duchy of Cornwall’s 67,500-acre share of Dartmoor National Park is among the royal properties charging “feudal levies”, according to the investigation.
It bills the British Army an undisclosed sum each year for the right to train on the land under a 21-year deal struck when the King, who is now the head of the Armed Forces, was the Duke of Cornwall.
Prince William’s duchy has also charged the Ministry of Defence at least £900,000 over the past two decades to moor boats on waters surrounding the Britannia Royal Naval College.
Generations of male royals spanning back to George VI have been taught at the college, which is used to train British naval officers.
HMP Dartmoor, a category C prison for 640 inmates, also earns Prince William millions each year. The heir to the throne’s duchy signed a £37 million deal to lease the prison for 25 years to the Ministry of Justice, which is also liable to spend at least £68 million over the next decade updating the site’s buildings.
The royals also earn money from state schools, underground mines, pubs, car parks, and even a portable toilet supplier that sit on duchy land, according to the investigation.
The Duchy of Lancaster’s coastline assets will also earn the King £28 million over the next 50 years through cable undersea charges for wind farms.
Meanwhile, a 1960s tower block in London owned by Prince William’s duchy has brought in at least £22 million since 2005 from rents paid by charities and other tenants. It includes two cancer charities, Marie Curie and Macmillan, which counts the King as a patron. They both recently moved out to smaller premises.