Ecotricity have been recommend by Which? magazine.
They are know for investing in new renewable supply, whihc they brand as "Bills in Mills". As well as onshore wind, they have developed an anaerobic digestion plant fed by grass, that creattes BioMethane, as a Green Gas alterntive to Methane, to inject into the gas grid.
The company founder and owner is Dale Vince.If you use Facebook then there is an unused Ecotricity forum group.
I will also added related links including biomethane below.