I live in the UK, though not in London. I can count on one hand the number of times a group of children asked me to buy alcohol for them. So it's not that it doesn't happen, but it almost never happens.
Compare standing outside a supermarket, repeatedly begging passers by to commit a crime for you every time you want alcohol, with the one time action of installing a VPN client on your device and it's obvious one law is enforceable while the other is not.
What? - I live in London, if you walk through a high street where there is both a secondary school and a corner store (if you say you don't know what that is, I will assume you are Trump) at around 3-4pm - you either get asked to buy cigarettes; or, refusing to do so you will get asked if you have any cigarettes. Without fail.
You are trying to make it dramatic by saying it is a crime - in this context installing a VPN is as much a crime (arguably with more traces / evidence) as buying cigarettes for teenagers.
It is not. There is no law against circumventing age gates by means of a VPN. It is illegal to promote VPN services to children as a means of circumventing age gates, but the act itself is not illegal.
