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 want to try Ecotricity use code: Q9S4A7 to get £50 per fuel credit when you sign up with them, but they seem to often have better sign up offers on their website anyway, perhaps you can use both. If you use Facebook then there is an unused Ecotricity forum group.
I will also added related links including biomethane below.