Credit of £20 every day?? Seems a bit generous.
Nah, the £20 a day isn't sustainable, that's just a test to see if people would be up for it.
Reducing load at the peak time would be worth £3 per day to lots of people though, and would bring bills down for everyone as the energy demand becomes much simpler to manage. Lots of poeple won't care about £3 a day, they won't even notice, and would not be interested, some others would do it for the good of the UK, and not for the money.
You wouldn't want everyone doing it though, as it just moves the high load, from one time to another, but moving some of it, to level off demand and maybe also cutting some use really helps.
It's like the below, the white line at the top is total demand, the yellow line I added would be the ideal, easy to predict, but generation wouldn't match this in the future as it's not sunny on a night, and I think it's less windy too, so the red line I overlaid would be more their target, I expect.
The red line below it is how they have to shift the gas (and other fossil fuels), up and down, which probably isn't effient.
When more solar and wind comes more on line, they're going to want everyone moving use to that, in the day, when it's sunny and windy, rather than figuring how to store the wind energy for later, and then re-distribute that, which won't be as reactive, will be less effient and will have more cost. There will be other generation methods used throughout the night, lokoing after the base load which won't go away (nuclear, energy from waste, gas running at a constant (much lower) level until we get away from it etc).