They are not compulsory. You may refuse.
For now, but for how long ? I can see two long term results ...
Either it's seen as the complete balls up that it is, or it'll become optional in theory - but the only tariffs available for non-smart meter installs will be "unaffordable". I'll certainly be using "firm responses" to anyone suggesting I should have one.
Now I may be wrong but I was lead to understand the smart bit is being able to detect direction of current flow.
It's nowt to do with that, current meters do that, even the older Ferraris disk meters can do it (AIUI they have mechanisms to prevent reverse-rotation). The smart bit is in two bits :
Firstly they are multi-register - in principle they can meter up to 48 different rates in one day (a different price for every half hour !). Plus they can other tricks like "the first x units at y rate, then the rest at z rate".
The second, and main feature, is the remote controllability. Primarily this is about remotely setting the mode (credit or pre-pay) and charging rates, plus the ability to apply short term over-rides. In extreme, they also allow remote supply disconnection - and of course we all expect that there will be no administrative errors when disconnecting supplies
Coupled to this is the ability for them to communicate to in-premises devices. The idea is that instead of running the washing machine and tumble drier when we're about, we'll program them to only run when the lecky is cheap (because demand is low and the wind is blowing when it's not needed). Of course, running the washing machine and tumble drier at night has no issues - we love having the upstairs neighbour running their spin cycle at 2 in the morning when we're trying to sleep, and such appliances are known to be so very reliable and not prone to fires
But a lot of it is predicated on people watching the display and working out that it's going to be expensive to cook the evening meal at the normal time (because we've got insufficient supply when the wind isn't blowing) - so we'll wait for a few hours before eating.
Claims of people saving energy are just greenwash to try and make them sound useful - people who understand such things have found that initially people cut demand, but within a week or two their lecky usage is back to normal and the display is thrown in a drawer.
Smart meters are really an admission that they've given up on trying to provide supplies to match demand, and now are managing demand to match supply - thanks to all the money we're p***ing up the wall on windmill subsidies.