Nuisance email

Questions:

I am getting a lot of unsolicited e-mails, is there anything I can do to stop them?
I have seen a website condoning/encouraging violence against certain groups of people, what should I do?
My friend/ex partner/ex employee is sending me threatening/nuisance e-mails/texts/phone calls, what can I do?

Do I have to have my car insured if I don't use it and it is parked on private land?

For police non-emergencies dial 101