Thats why they invented MANPADS. Hell, thats why they invented shotguns.
If this happened in the United States they would be conducting a postmortem on the pilot. I would hope that the security for Theresa May is good, but I doubt it.
That para-glider could have 100 lbs of high explosive on it.
Or one of these...
https://www.bing.com/images/search?q=phalanx+weapon+system&qpvt=phalanx+weapon+system&FORM=IGRE