Details about the royal family's finances including rent received from the NHS, schools and the armed forces have been revealed as part of a new documentary.

In the investigation by Channel 4's Dispatches and the Sunday Times, it is reported that the private estates of King Charles and Prince William have received millions of pounds of income from contracts with public bodies and charities.

Over the past year these deals with the Duchies of Lancaster and Cornwall have been worth almost £50 million, it has been claimed.

A spokesperson for the Duchy of Lancaster, the private estate of King Charles, said it "complies with all relevant UK legislation and regulatory standards applicable to its range of business activities".

The Duchy of Lancaster, established in 1399, and Prince William's Duchy of Cornwall, established in 1337, both hold large amounts of land and commercial property in England and Wales.

Their contracts with public bodies are said to include a £37 million agreement between the Duchy of Cornwall and the Ministry of Justice to lease Dartmoor Prison, and a £11.4 million deal between Guy's and St Thomas' NHS Trust and the Duchy of Lancaster to rent a London warehouse over 15 years.

The programme, Dispatches' The King, The Prince and Their Secret Millions, reports that details of the rental agreements have not been given to Parliament.

The documentary raises concerns about the environmental impact of some of the estates' contracts, including those with mining companies.

The two private estates are separate to the Crown Estate.

Profits of the Crown Estate - a property business owned by the monarch but run independently - go to the Treasury. The level of profit made by the Crown Estate is used as a benchmark to calculate the funding given by the government to the Royal Family in the form of the Sovereign Grant.

The taxpayer-funded Sovereign Grant will rise to £132m next year, after profits from the Crown Estate increased to £1.1 billion.

A Duchy of Cornwall spokesperson said it 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".

On the issue of mining, the spokesperson said that the duchy was "acting responsibly and in a sustainable way" to the government's industrial strategy.

A spokesperson for the Duchy of Lancaster said it operates "as a commercial company, managing a broad range of land and property assets across England and Wales".

They said that the duchy "delegates certain functions, particularly those regarding asset management, to the Duchy Council" and while the King "takes a close interest" in the work of the duchy, day-to-day management of the portfolio is the responsibility of the council and executive team.