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.

It added it had made “a number of key environmental improvements in recent years”.