If all the porn sites blocked UK traffic over night, there would be a revolution the next morning.
Discussion
Porn sites won't do anything they've made it really easy to work around it just for accessing porn. (At least in Australia this may not apply to UK but I just assume)

Gonna be a looooottttaaa overflowing goons ππ
There are two kinds of men: those who watch porn and those who lie about watching porn. πππ
I believe most porn sites have put an age verification wall up for UK. Or do you mean block entirely?