UK Gov is always pushing for similar. They tried to get an age requirement system before. Currently it's the online safety bill. Most ISPs run some sort of filter by default, for example on 3, this site, https://www.ukbumpkeys.com/ will silent error as unreachable, not an error that its being blocked by 'safety' filter. Wouldn't be surprised if they follow China and expect any site with an online comment section to do KYC at some point.