One tweak to the rules and all of a sudden not only do porn sites have to verify the age of their UK visitors but also anyone connecting from something other than a residential ISP.
The more troubling thing about these laws is enforcement. The threat of fines only works against websites that map to a business entity. For anything else there will surely see a ramp up in the size of The Great British Firewall Ruleset, edited by the courts, and distributed to the Big N (5?) ISPs.
What will become of the smaller ISPs that refuse to block illegal sites?
I've found Tor is mostly useful for reading, not participating. Exit nodes get blocked from registering on most sites. One workaround is to register at a café or library then use the account over Tor, but sometimes even if you're being civil (see my comment history for a a pretty good picture of the style of discussions I have anonymously) sometimes you'll wake up to find the account nuked.