You are correct to point those cases out, and I am aware of them. It was also outrageous to infiltrate the MLK movement. Not to downplay those cases, but there is a distinction between these cases with the FBI and the current case with London police: The London police is a local enforcement agency. When local police forces start actively hacking citizens there is a different kind of danger than when a federal agency does so, mainly because they have different enforcement interests and powers. When a local enforcement agency begins to spy and hack, that is a new level of harassment and violation of civil liberties.

As a technique, it goes waay back. There is some reason to believe even the Gunpowder Plot was engineered by authorities.

I'm confused by your post. We see that these police had extensive legal surveillance powers available to them, but chose not to use those and to break the various laws to illegally spy on these people.

Rule of law guarantees law will be applied, not that people rights and freedom will be upheld.