I don't think that's true. Energy suppliers have to sell at a price higher than they can buy it at. Energy suppliers are not necessarily energy producers as well. If you cap the output price but not the input price then there is no scope to stay viable. That is why so many of them have gone bust.All the energy companies treat the price cap as a target not a cap. It’s ridiculous that no matter how cheaply we can produce gas for our own domestic market the global price is the deciding factor.
Its interesting to see what the prices are on the Octopus Agile tariff. These track the wholesale price at 30 minute intervals. A year ago there were times where the price went negative ie you were paid to use electricity. Over the last month it has hit the cap (at 55p unit) for most time periods. This also gives a clue as to where the next general cap will be and it won't be below 55p/unit unless they play fast and loose with the standing charge.
Market forces dictate that as a producer you sell to the highest bidder, especially as there is a bunch of market makers in the way. If you want to control prices you also have to control the market makers. Tricky as its now an international business.
Taxing the producers is one way of doing it, but you can only tax those that pay tax in your country. Otherwise the only option I see is to nationalise production in your own country and monopolise the local market. That requires you to have enough resources to supply 100% of what you need for all requirements. I'm not sure we are in a position to claim that.
If you want to cap the market for political reasons, then the government will have to subsidise the suppliers, because the original problem hasn't gone away. That is achieved by either higher taxes or higher borrowing.
Its a global market and we have no control over it, as far as I can see. Am I wrong? I hope so!