Basically, in the UK, you used to need a gun license to hold any weaponry.
A known paedophile called Thomas Hamilton managed to get ahold of one despite being told no several times with the help of one of his friends… no other than George Robinson. The tenth Secretary General of NATO. As in, the none-American chief of NATO.
Robinson's kids all went to Dunblane primary (a small Scottish town) which is where the shooter went. He was a sports teacher of some kind and several members of staff had accused him of touching up kids. He shot primary school kids and then Robinson campaigned for the banning of almost all guns in the UK. That's why the guns are banned here.
Of course, this is why you Americans should NEVER FUCKING ASK FOR GUN REGISTRATION. It is only the first step. It happened here and somehow, a known nonce (who was hated by the town - which is why he went and shot all of the kids) managed to get a license. After which, all guns were banned except double barrelled shotguns and antiques.
It didn't work and now gun crime is higher than ever.
Former PM Gordon Brown is also somehow connected. I don't know how, off the top of my head.
Incase you were wondering why Trump went after NATO, by the way, it's because they're not exactly the benevolent saints our politics make them out to be. They're infested with the same hook-nosed gentlemen, nonces and crooks that infest Washington.
There's a reason why nobody in the USA mentions exactly why the UK has a gun ban. It's because it raises some rather inconvenient questions and would likely push Americans away from the idea of gun registration.
Anyway, back to Hamilton.
Several of his neighbours reported that on the morning (March 13th, 1996) he exited a "posh car" smiling.
He was not the driver.
The entire town said that he had some "Toff" (British slang for rich, or well-off) friends who he would speak with.
This is the tip of the iceberg, I'm afraid.
A former headteacher of the school was found having accidentally slipped in the shower onto a rope, or some weird shit like that, and a dorm manager or something quit after two years - citing Hamilton, a sports coach (or gym teacher or w/e Americans call it) was allowing "strange men" into the dorms where the kids were (in a school which Hamilton sorted the outgoing trips of - a different school to the one he normally worked at, which he shot up, Dunblane Primary).
This is a VERY important event in British history, by the way. I have a sickly feeling that this is how you Americans view Sandy Hook - because it gives me serious Dunblane vibes and this is the ENTIRE REASON WHY the left is pushing "gun registration" - because it's doomed to fail.