This is sounding unpleasantly like a re-run of Government versus Encryption
Remember all the calls for encryption products to have a back door in them for the use of police? Remember how our Government are completely sure that this is a good thing, completely sure that nobody will abuse the back door and utterly certain that nobody will do horrible and illegal things like install non-backdoored software?
This is more of the same.
This is politicians trying to change reality by averring that such a thing is so, when in fact it is not. Age verification absolutely has to identify the person who is having their age verified, otherwise it is useless. Therefore age verification will identify who looks at what, and said details will be stored on a government computer somewhere, and later lost on a train by some gormless civil servant.
Anyone with any sense will therefore give this age verification system the bargepole treatment, and obtain a VPN from an off-shore supplier. There are lots of different VPN suppliers to choose from, quite a few of which keep no records of what traverses their systems whatsoever.
Somewhere, therefore, an MI5 man is crying into his beer as formerly passable sources of Internet metadata go opaque. Even the fact that someone was using an off-shore VPN was (and probably still is) a useful indicator of either paranoia or nefarious deeds (barring business use, of course).
Alter the pr0n laws so that a VPN becomes a necessary adjunct of anyone who fancies a spot of executive relief, and all of a sudden VPN traffic becomes so common that it isn't a marker of dodgy deeds any more. Hey presto, that's another easy source of intelligence ruined by the politicians.