Can you give an example of a better method?
The one that I can think of is the government sets the amount of electricity produced, and then it’s rationed. But I doubt the UK would be happy with rationed electricity where your power shuts off the second it’s over. That would be essentially mandatory blackouts all the time.
Not to mention the cost would be held by the government, so you end up paying it in taxes anyway.
Rationed electricity might also come in the form of a universal basic entitlement, followed by market price for higher usage. One assumes under such a system that the state would own and operate energy production and that they would, for instance, increase the ration over time, leaving the remaining needed capacity to be fulfilled by the market.
Honestly, pricing based on the cost of financing and operation isn't a terrible idea.