The issue is that the energy markets aren't regulated, or at least regulated effectively.
Of course it shouldn't have been privatised in the first place (another Thatcher economic policy that failed), but save for that then the next best arrangement is the state becoming a majority shareholder, similar to France.
It cannot be right that rising costs are entirely passed onto consumers, thereby protecting (already eye-watering) profits.
It's the biggest problem of a free market economy and a conspicuous example of why the markets need proper regulation.