This law is supposed to only affect "commercial" sites, see the first three paragraphs:
External Link/Members OnlySo strangely if a site is proven to be 100% free then it makes it outside of that law and could have hardcore videos open for all. You'd expect them to realize their "flawed" law and a future law to "fix" that.
A government document published (can't find link) makes it clear that a site will be regarded as "commercial" even if it was free should it have adverts, i.e. PornHub makes it money from adverts, so it is included. Free sites that make affiliate income / earn a commission from referring sales to another commercial site are again included.
The quango BBFC says even if a site didn't have pics or video than just the text alone can make it require age verification, it's all about whether the content is
"produced
solely or principally for the purposes of sexual arousal".
So whether UKP is affected is a grey area. Despite UKP being 100% free and without a single advert, either free or paid, the quango could find it hard to believe, you can see even some punters, prossies and pimps find it hard to believe.
Again whether agency or parlour sites are affected is a grey area. I guess they will remove nude pics just to be safer.
Regarding giving credit card details, another quango, ATVOD, say age verification can be done via SMS text message, because a site operator can restrict their txt message so it wouldn't be received by a non-age-verified SIM card. This is what PornHub plan to do according to one of their staff. BBFC of course could disagree but I doubt it.
On the topic of VPNs, a number of countries ban them already, for example a law was passed in Russia that forces VPN providers to block sites. Tor is blocked in China, even hidden entry nodes get blocked pretty quickly, it's all automated and works very well. China sells this "technology" to other shitholes like Iran. Expect similar laws in UK in future, see my below previous post about UK's gloomy future regarding prostitution, Internet censorship and government control.
But I feel there is a mistaken assumption things will stay as they are. The way things are going politics wise in UK from what I read, I wouldn't be surprised in the 5-10 years punting will be made illegal in UK and the politicians will go max into internet censorship, forcing internet providers to block not just punting sites like AW/UKP/Vivastreet/Backpage, but Bitcoin, Tor, VPNs, P2P, BitTorrent, etc. They will use the usual excuses of - terrorism, child safety, trafficking, tax evasion, and the new excuse of "Russia meddling in democracy with fake news".
So punters will have to resort to good ol' email to exchange punting info, but that's until UK government outlaws all email providers who don't allow them to read your emails. This is not far fetched given the UK government is demanding the likes of Whatsapp and Telegram to provide them a backdoor in their apps so they could disable end-to-end encryption on UK citizens and spy on their conversations.