“Spontaneous” responses to terrorist attacks are coordinated by the UK Gov

From 2019, and this reeks of stretching too few facts too far. All major governments are going to create contingency plans, with probability of that contingency coming true from 100% (major fire) to 0% (something like "UFO attack"). If as much prep was done as is stated (posters designed and printed, ecumenical statements negotiated) this would already have leaked. Three may keep a secret, as long as two of them are dead, as is well known.