Warn the UK users during the grace period as best as they can.

And after the grace period... yeah, I think blocking UK IPs is the "correct" thing to do. If the government doesn't make them an exception than they'll have to do that, correct or not, anyway.

I think the people of the UK have little or nothing to do with this.

UK is a representative democracy meaning that voters get a voice every X years to vote for a representative that they assume will act in their favour and on their behalf.

What this representative does in their time in power is very much left to the representative and not the voters.

On the other hand, if this were to be a direct democracy then the voters would have been asked before this law was voted on. For example, a referendum might well have been held.

Perhaps a more nuanced approach would be to block all IPs of government organisations - difficult but far more approriate.