Yes, I always assumed it was to shoot them down if they had no choice
I saw/heard it, too. I was trying to get DD out of the car into the house without waking her up and had to wait until it had gone. Very, very loud and a bit scary because the clouds were thick and I didn't see the jet for a while. It must have gone right over me at one point.
You know what gets me, both of these cases recently (there was one last week in US I think it was) they left the plane on the tarmac for hours until armed police got there. On the Manchester one they did not say why but on US one they did.
I fully get why but I do not want to be kept on any bloody plane on the ground which might have a bomb on it for hours with my children.
I would want off!!!
Terrified of flying and flying from Manchester soon.