Next time you flush the toilet, you could be doing your bit for green energy. After being stored for 18 days, human waste will from today be returning to homes in the form of renewable gas.

Centrica is opening a plant at Didcot sewage works which will be the first in the UK to produce renewable gas for households to use.

National Grid believes that at least 15% of all gas consumed could be made from sewage slurry, old sandwiches and other food thrown away by supermarkets, as well as organic waste created by businesses such as breweries.

However, there are fears in the industry that the government's spending cuts could make it more difficult for companies to come up with the £10bn needed to develop the new plants and pipelines.

Because it is more expensive to produce renewable gas, companies say they need to be paid twice the market rate for it to make economic sense.

But a proposed subsidy, scheduled to come into force in April, has yet to be approved and there is speculation that the government could delay or scrap it.

The Didcot facility is a pilot project to demonstrate the technology and will supply about 200 homes with gas. The project is a joint venture between Thames Water, British Gas and Scotia Gas Networks.

One industry expert likened the process to a "cow's stomach on a life support machine". The sewage sludge is collected in air-tight vats which are heated and enzymes added to speed the anaerobic digestion process and break down the material. Methane is produced and then it is purified ready for use.

Landfill sites can also produce methane gas which is then typically used to generate electricity. But British Gas says supplying renewable gas directly is much more efficient, as about two thirds of the energy is lost when electricity is generated.

This Friday, Adnams the brewer will open an anaerobic digestion facility in Suffolk using waste slurry which will provide renewable gas to about 235 homes. British Gas is also involved in this project and is planning to open three more.

Gearóid Lane, managing director of communities and new energy at British Gas, said: "This renewable gas project is a real milestone in Britain's energy history, and will help customers and the environment alike. Renewable gas has the potential to make a significant contribution to meeting the UK's energy needs. Gas from sewage is just one part of a bigger project, which will see us using brewery and food waste and farm slurry to generate gas to heat homes."