If people are going to let themselves get screwed by sticking with their supplier and not even checking that supplier's tarrifs, frankly that is their lookout. But then as an old-fashioned liberal I'm as against government mollycoddling of consumers as I am against government regulation of pretty much anything - within reason of course.
In the early days of electricity privatisation, it was easy - your default local supplier was always the most expensive, because of customer inertia. You got stuck with the default supplier when you moved, so simply cancelled the contract and changed to anyone else at the earliest opportunity you had to get out of the default contract. I don't know what it is like now as I no longer live in the UK, but generally similar conditions apply here in Germany, where the domestic energy market is still in early stages, relative to the UK, of liberalisation.
All utility tarrifs boil down to two components - standing charge and charge for the quantity used. It's quite straightforward to work out which is the cheapest, there are even websites that will do it for you.
Here there is a complicating factor introduced by companies that will sell you cheap energy if you pay a year up front, but the "cheapness" only comes because you effectively pay a bond and get it refunded at the end of the year. (And at the end of the year, if you don't cancel in time you get stuck on a much more expensive tarrif for a minimum of one year.) Of course, these companies allegedly never repay the bond absent a court order, and they know most customers will not go to court. They also have a nasty habit of going bankrupt as they are so cheap they have to fund existing customers consumption by getting more customers - a Ponzi scheme in other words. There I can see a case for regulation.