Poundbury is set to become Britain’s first urban extension to switch to ‘green’ gas.

The Dorchester development’s eco-friendly project will be powered by decomposing crops.

When up and running, its anaerobic digester will produce enough gas to supply 4,000 homes in midwinter and up to 56,000 in summer.

It is expected to be ready to supply residents of Prince Charles’ model development by September.

The digester is based at Rainbarrow Farm in Martinstown and was set up by the Duchy of Cornwall with four farmers and a business strategist.

Gas is already being sent to Poundbury through underground pipes and will be burned to produce electricity for 750 homes.

A plant will be connected to clean the gas so it can be used in domestic boilers and cookers. Crops are now being grown especially for the digester.

The scheme will qualify for feed-in tariffs – subsidies offered by the government to green energy suppliers.

Nick Finding, a Duchy tenant farmer and scheme member, said: “The system is now built and waiting for connection. Charles has been involved and came to see the project.”