The UK tweet thing was a crazy overreaction, yes.
In all honesty though... wouldn't you be kinda surprised if law enforcement wasn't monitoring social media? Not looking for the super secret terrorist cell mind you, who probably would refrain from tweeting before their grand operation. But looking for the bat-shit loon who decides to use whatever hater theory is au courant as pretext for their batshit loontastic ideas. E.g., shoebombers.
What citizens/journalists should be vigorously investigating is not whether the social media monitoring is happening (cause it is), but whether those Personally Identifiable Information rules are reasonable, whether they are being followed, and just how many people are on the terrorist/drug (i.e., the "perpetual wars" (/eyeroll) we are fighting) lists, how reasonable are the names on those lists, etc., etc.