The thing is, the attacker was apparently “known to police” and “had been previously investigated for terrorist ties”.
“Raids were conducted around London and other cities in England” means that the police KNEW who was a threat. Knew that there were people who were a danger (otherwise how else would they know who/where to raid. Which means they knew who were the rattlesnakes living in the midst of the citizenry…..and allowed those dangers to fester until 4 were killed and other injured.
Why allow these folks to live in the country when they know they are dangerous?