Earlier quoted context omitted.
No, consumers will likely be paying the capped price. (A regulator on behalf of) the British government sets a six monthly price cap, based on the actual prices from a historical six month period, ordinarily this cap just means that people who are too poor or too lazy to "shop around" for a better deal pay no more than this amount for their electricity, but because the UK uses a lot of natural gas to make electricity…
Which raises the question... Can I as a consumer put a big pump in my back yard to pump water uphill (paying the price cap), and then own a company that generates power from the water flowing down the hill, and get paid wholesale rates, profiting from the difference?
By the time you're moving enough water to get a wholesale contract to sell your power, you're also going to need to buy enough electricity that you had to sign a wholesale contract for that and now you're just another small energy storage company, you are competing with the hollow mountain and all the startups who've bought a lot of batteries and a building on an industrial estate near a big transformer. You could doubtless make some money, this is a growing industry and enthusiasm goes some distance but you aren't going to get away with having a capped consumer supply contract and then selling that as wholesale electricity.