I understood a problem that energy providers are investing some minimum (perhaps only the legal minimum) into green provision, an amount that they would have an

I understood a problem that energy providers are investing some minimum (perhaps only the legal minimum) into green provision, an amount that they would have anyway. And, selling this onwards as a premium to the end user without actually changing their behaviour. Since you get the same service (your power ultimately comes from the same grid), it's a pure price discrimination strategy. [This is maybe a general restatement of pjerem's sibling comment] I do pay this premium, but I mostly feel cheated by it.