I think the Online safety bill in the U.K. has been watered down a lot since its inception. I’m not sure age verification is even a part of it anymore. What was being mooted here though was that your age would be verified by a company online but your details would not be stored and they wouldn’t know what site you were seeking it for. For example, the same company could be doing this for online gambling sites so when asked to verify you, they wouldn’t know it was for porn.
The other option was that you would go into a store and buy an anonymous age verification card. It would cost something like £5.00 and the person behind the counter would verify that you were over 18 before selling you the card like they would if selling you alcohol. This card would have an anonymous code you would enter online and this would prove to the site that you were of age. In that case it’s all pretty anonymous except you actually have to go into a store and announce to the guy behind the counter that that you’re a big perv!