[1] https://www.gov.uk/government/publications/pm-letter-to-nati...
Surprise!
I'm trying not to argue for or against opt-in vs opt-out or no choice, that's a fine discussion to have, but this thread was more about notice.
It's more important to tell people when the green and white papers are being read and when the bill is being discussed, and then when the law is made, and there was a lot of publicity then.
The comparison is also moot because there is no opt-out of a law which forces you to wear a mask, or forces you to get vaccinated. There is an opt-out regarding organ donation. A comparison would be, that you'd be forced to wear masks everywhere, and that you'd by default get vaccinated, but you are free to decline (opt-out). Well, vaccinations in The Netherlands already work like this. Your kid gets asked to get a vaccination, and you are free to decline it. You don't have to ask the government for it though. That's opt-out as well.