I would agree that concealed carry wouldn’t do much in this case as it is really hard to stop a drive by shooting of this type. So yes all the people beating their chests and saying it would be different in the US are not thinking, just look at what happens in the hood, most gang bangers are armed AND expecting a drive-by to happen but rarely have time to react, other than diving for cover. Certainly in rural UK (or in most of the rural US) you are not expecting something like this to happen and even if armed would not be able to react.
The real question is what caused this guy to go postal? My bet is he was on some sort of anti-depressant or Prozac type drug or just going off of it. These drugs ARE more dangerous than a loaded gun because of these types if reactions. Most mass shooters in the US were on or going off of these type of drugs. Unfortunately there will be no call to ban the drugs but most likely a call to ban shotguns will definitely be heard after this.
The latest information that is coming out here is that three of the victims are the shooters own mother and twin brother and the family lawyer. There is talk of some kind of family dispute involving a will. Who can say? No doubt more information will emerge with time.