The method uses biogas, which is produced when waste water sludge is broken down by microbes in a process known as anaerobic digestion.

BBC: United Utilities turns human waste to energy at plant

Protesters say fracking could have "enormous implications" for the local environment particularly about the contamination of waste or flowback water once it has been used in the fracking process.

BBC: Lancashire's shale gas estimated at ?136bn by Cuadrilla

Vivendi is a media, telecoms and Internet company still in the process of emerging from its origins as a state-owned water-and-waste utility.

ECONOMIST: Vodafone/Vivendi/Mannesmann