According to a press release, recent figures show that the London's Royal family has cut carbon emissions by 2818 tonnes — equivalent to the environmental benefits of planting 4,332 trees — by making its own electricity.

According to latest data from green power business Ener-g, a UK-owned sustainable energy technology business, the Royal households have created 13 million Kilo Watt hours of electricity, sufficient to make 130 million cups of tea - more than two cups each for every man, woman and child in the United Kingdom.

Buckingham Palace and Windsor Castle use energy efficient combined heat and power technology to generate their own electricity and heat. This method is more efficient than traditional gas power stations because it captures the heat that is normally wasted and avoids transmission losses because the energy is generated locally.

Peter Law, a director of Ener-g, which supplied the power system, said: "The Royal household decided to install the technology because of its environmental benefits, but has also benefited from cheaper electricity".

The Windsor Castle installation was a feat of British engineering, being built at Ener-g's Manchester factory, before being stripped down, shipped to Windsor Castle and then re-built in the former dungeon. This machine also acts as an emergency generator in the event of a power failure.

The Royal Household has been working on reducing its energy consumption for the past 22 years. A time-line showing the introduction of a variety of energy-saving initiatives since 1985 is available here.