Signing up to a four-years-gone ex-pupil's erotic (sometimes schoolgirl-themed!) website as a live-in boarding school teacher is absolutely is not the same as hiring an ex-pupil to service your boiler. Sex work is not identical to other work. People can pretend it is, but it is not - that's a whole other huge topic of conversation.
People bleating on and on that he's entitled to buy her services need to raise their expectations of men and teachers. No normal, reasonable teacher would ever do this; any colleagues would be appalled to learn it and the parents paying to send their children to this boarding school would be rightly up in arms to know what he's done.
A school with robust safeguarding policies and a good DSL would absolutely act on this.
Him using the school address would make it easy for the school to act - this will be a breach of his contract.
I don't know about the privacy aspect but it's pretty bleak if a man's right to privacy overrides the safety of the girls he teaches.
A lot of the defence of this creep for pages insisted that he probably didn't recognise her, it was all coincidence, no one could say he has a thing for schoolgirls, this isn't deliberate etc etc. All of that is blown out the water, plus it turns out he's living alongside students and he's using the school address but still people can find reasons to excuse him. It's inexplicable to me that anyone would prefer to defend a man like this than uphold the right of girls to be safe in school, or that anyone would be happy to have this creep in the same classroom as their own daughters.
I don't want to Google Daily Star page 3 girls! But if it did end in 2019, how does that work OP?