Not illegal.
I guess, it depends. I wouldn't want it removed unless it has realistic risk of making someone harm me. It would serve as a record that I can use to build my narrative when discussing stuff.
Is it an organised campaign? Is it you being targeted because of who you are? Is it happening on 4chan? Is it happening in a whatsapp group? What are the nature of the content? Do they claim stuff about you? Do they threaten you? Are they writing alternative history?
Simply deleting doesn't help with anything. Remember PewDiePie who was cancelled for making antisemitic jokes? He probably didn't know what he was doing because of his perspective there are no more nazis around and all that stuff is history from 50 years ago so it's just a joke. Deleting content gives the impression that these don't exist or that it's not a real danger.
Meanwhile a history teacher and film maker on youtube dresses up as a literal nazi in several videos, including swastika, and does not get cancelled because it's pretty good satire.
Freedom of speech means you get to tell any joke you want, but freedom of speech does not mean people have to treat your actions as a joke just because you meant it as a joke. You don't get to be the sole arbiter of the "goodness" of your actions, because not meaning to hurt people doesn't let you off the hook for hurting people.
IMHO no content should be removed unless the existence of content creates tangible issues. For example hosting copyrighted material creates the issue of copyright holders not getting paid for their work, therefore removable but the record of someone saying saying something bigoted doesn't actually harm anyone(if there's a harm it has been done at the moment of expressing it) therefore should not be removed and kept as an evidence of the character and actions of the person. Any content is a historical record, thanks to that we can look what Hitler said and we can reason over it and know why he is despised. This gives fidelity and understanding of the situation. We don't say Hitler was bad because he violated rule 4.1 in the TOS, the same must be true for everyone.
If UK does something like that, it can be a huge win.