Why don't you just Google "uk man arrested for tweet" and you'll find plenty.
From the Verge[1]: Section 127 of the Communications Act makes it an offense to send public messages of a “grossly offensive or of an indecent, obscene or menacing character,”
Do I think threats are acceptable, no - and true threats aren't considered protected free speech. ("true threats first amendment" would be your search term, should you like to learn more)
Do I think offensive, nasty, hateful speech is free speech? Absolutely.
You think that's ok? One of them for reference:
"kill yourself before I do; rape is the last of your worries; I’ve just got out of prison and would happily do more time to see you berried.”