So instead you would prefer Police officers that enforce laws as they see fit and not as passed by democratically elected Legislatures and/or interpreted by an independent Judiciary?
That is a DANGEROUS road to go down because what laws to enforce and when is a recipie for abuse. I can't speak for the UK as you note specifically but the way you address your fear of being arrested for violating a law is via organizations like this Knife Rights - Home which have gotten knife laws changed at the State level to include laws forbidding individual Municipalities passing laws that contradict State Law.
That poster hasn't been here for five years now, he gave the impression that he was being oppressed but I doubt it very much. I also doubt he was in the UK to be honest but there you go. These days we have bigger things to worry about than knife or cannabis laws, trust me we really aren't that bothered.