For John, BLUF: When the attack is happening around you, the police may be only a 911 call away, plus travel time. Nothing to see here; just move along.
We are looking at a "potential" terrorist attack in London.
The British Prime Minister, Theresa May, thanked the First Responders.
The problem is that she has misidentified the First Responders. The First Responders are NOT the Police, Fire and Rescue organizations of the local authorities.
The First Responders are the folks at the scene as the attack in taking place. For example, the people in a restaurant who where throwing things at a knife wielding attacker, in hopes of driving him off after he knifed a restaurant patron.
Of course if we realize who the true First Responders are then someone will ask how we help them. I don't know what the U.K. Can do, but we can be more open about the Second Amendment.
Regards — Cliff