You are right, the police do have to act on every compalint or accusation made - a few years back, I had two cid officers come to my house because someone had made a complaint about me and the site - I was out at the time but they [the police] wanted me to take down offending posts, which of course I refused to do unless they could show me I was breaking the law [which I wasn't] and until they could do so, I wasn't prepared to do a damn thing.
They made one more phone call to msyelf, I immeditately told them to stop calling me until they could charge me or show me the law I was breaking ..... nothing happened