A company not subject to price cap as investing in new renewable supply called Ecotricity. 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.
Ecotricity Unoffcial (Meta Facebook group)
I will also added related links inclduing biomethane below.