[londons_explore]

Technically it's easy. The complexity is all with laws and commercial interests.

There are hundreds of thousands of residential batteries in the UK already, and ~0 of them currently can be called on for demand frequency response. That's because 'demand response' is not something you can typically be credited for on your electricity bill. The closest you get is you might have a half-hourly varying pricing scheme encouraging you to discharge your battery when prices are low. The only UK supplier to do that so far (octopus) still uses day-ahead prices though - so you aren't reacting to market conditions, but instead predicted market conditions 24 hours ahead.

I think the fix for the uk is for the regulator to step in and switch half hourly pricing for second by second pricing. Get rid of 'frequency services' (unnecessary with second by second pricing). Then make most/all users of the grid pay those second by second prices (no more 'fixed X per kwh' contracts).

All electricity contracts should be pay-in-advance, and meters should have an option to cap spend per hour/day.

[whatevaa]

Nobody wants to spend their time micromanaging their electricity usage to such a point. Such a scheme to all users will never pass. Lack of day-ahead means it's impossible to plan anything.

[londons_explore]

You can still plan based on day-ahead prices. And just take the risk on the difference between day ahead and spot pricing if you like. And if you don't want to take that risk, you can buy contracts for difference between the two from someone else willing to take on the risk. And if you don't want the hassle, you can sign up with an electricity provider willing to do all of the above and not even tell you about the complexity of such stuff.