Then the bill payer can enable or disable access for three categories
* Under 18s
* Over 18s
* Unknown
as they are the bill payer and entering into a credit agreement requires you to be over 18. If you wanted belt and braces the phone companies doing PAYG could set it to disabled unless you authenticate your age to avoid the "buy simcard for cash" loophole.
ISPs could choose to implement finer grained controls in their routers. The majority of the big ISPs would likely block the "over 18" category by default.
The people writing these laws don't know about DNS.
This isn't really relevant because what is considered "suitable for under 18s" varies wildly per country. Some countries ban rainbow flags, others will happily sell alcohol to 16-year-olds. Plus, 99.99% of websites don't care about this and will be blocked by default if you block the "unknown" category. Grandma isn't going to call their ISP and ask to unblock pornography because the American knitting forum she's on doesn't know how to add TXT records.
Technical solutions don't solve political problems.
> The majority of the big ISPs would likely block the "over 18" category by default.
Existing UK legislation already requires them to do that.
[1] - https://www.rtalabel.org/index.php?content=howtofaq#single
This is already the case in UK, has been for years. The bill payer needs to prove age with an ID to lift IP level blocks from some default age blocklist.
It doesn't work well because obviously a lot of internet is shared amongst a household, and the blocklist is too broad to make it annoying enough that any adults will remove it. Then of course you can always just use a VPN same as with the current situation.
Putting the onus on the ISPs operating in the UK rather than the sites operating globally is much easier to implement than trying to enforce your laws on foreign companies.
That's if you want the outcome to block a certain list of sites by default.
As you say in reality we already have that. The question thus is what's the real point of the move, because it's not to stop 15 year olds jacking off.