It's pretty scary getting a phone call or visit from the police, but they make it quite clear you're not in trouble, at which point it's mostly infuriating that someone got butthurt enough to trouble you in this manner.
I can think of scenarios where it would be reasonable for the police to ask someone to stop legal behavior - "please stop pissing off your neighbours" - but this is not one of them.
It certainly wasn't suggested in the way the Mafia might suggest you pay for protection, if that's what you're thinking. There was no sense of authority when they asked it. It sounds like the same thing happened to OP.
I think that having the police, or a politician (http://www.washingtonpost.com/wp-dyn/content/article/2010/09...) or any other member of the government relay those requests is out of line.
The unreferenced ones are contentious, but from my understanding of UKIP's plans, they're broadly correct.
I think that he's confirming that some claims aren't verified because he's being honest, irrespective of party ties.
for context for non UK folk, the guy posting the story is a green (left of the center, strong environmental politics), and UKIP who are the current talk de jour in the UK are a rightwing nationalist party who are more acceptable in the UK than just blatantly supporting the BNP.
Oh, and if the police got involved, to be frank, assuming it happened like op said, that's absolute bullshit and basically intimidation. Considering the reach that tweet/poster image has had, I wouldn't be surprised if someone with connections within UKIP had pulled some strings to get the police to visit this guy.