That's why "market" isn't a good approach for electricity.
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.
Honestly, pricing based on the cost of financing and operation isn't a terrible idea.
Under the current system, when energy becomes hard to produce or more people need it, rising prices means people will reduce. So pricing for cost of financing, sure, but it might be a higher cost because people will consume more.