However, they received a payment of £1,471 from the National Grid for the electricity they supplied to the rest of the network. That meant their energy bills were wiped out completely and they made £764.60.

They have a rainwater harvesting system, which diverts water from the guttering into a 5,000-litre tank so it can be used to flush their toilets. As a result, their water bills – charged through a meter – have been reduced by about 60 per cent.

Mr Willcox, 66, a retired accountant, believes his home, which took ideas from house-builders in Sweden, could provide the template for hundreds of thousands of others. The property is super-insulated, built using 10in-thick polystyrene panels in the walls and roof.

Mr Willcox, 66, a retired accountant, believes his home, which took ideas from house-builders in Sweden, could provide the template for hundreds of thousands of others

The stunning property - including this modern kitchen - is super-insulated, built using 10in-thick polystyrene panels in the walls and roof

There is a ventilation system that pulls out stale air and brings in fresh air, eliminating draughts and damp. Mr Willcox said: ‘What we have done could be achieved by anybody in a new-build property.

‘If all new homes were built to this specification, or something similar, it would massively reduce the need for new power stations.’

The planning and construction of the home in Chilcompton, Somerset, which is called Tranquillity, took two years and the couple have lived there for six.

The land cost £170,000 and the building costs, including a detached garage and the eco installations, came to £350,000. That put the total cost at £520,000. However, the home is now worth more than £800,000.

The photovoltaic solar panels, which generate the electricity exported to the National Grid, cost £12,000. Based on receiving £1,471 a year from the grid, the cost is covered in just over eight years.

In fact, the contract with National Grid runs for 25 years and the tariff payments will rise in line with inflation, guaranteeing a good profit.