The 31 months was for literally inciting a mob to burn down a building with asylum seekers inside, in the middle of a riot. Yes, from the Internet rather than in person, and she's now very vigorous in claiming she didn't intend anyone to actually do it. But yeah. Likely criminal even in the US under the "imminent lawless action" exception.

Musk had bugger all to do with the rape gangs scandal, which broke literally years ago, and has been brought up with regularity by the newspapers here since. (For what it's worth there have also been plenty of non-Pakistani groups doing similar things and getting away with it. The main problem seems to be that no one in authority misses, or listens to, dropout teenage girls who have fallen off the radar - which makes them easy pickings for nonces.)

I don't know about the others. The sign holder was likely within the 150m buffer zone put around abortion clinics last year, though. Given the content of the sign (which just steps over the letter of the statutory prohibition not to influence patients' decisions while being entirely morally unobjectionable) I suspect it was a deliberate setup for arrest for outrage, just like the Palestine Action people. But I could be wrong.

It's perhaps also worth noting that Britain's traditions of free speech have never been as absolutist as the US (the last successful prosecution for blasphemous libel was as recent as the 70s and it's still technically a crime to advocate for a republic) but that raucous objections to government have very rarely been the target in recent centuries. The major difference in practice is that being grossly offensive isn't constitutionally protected. You're still not likely to get done for it, though.