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.