Tony got done for shooting them in the BACK when they were trying to escape, not when he was defending himself. He had an ILLEGAL weapon and had lost his licence prior ..... seems pretty simple to me.
Now before you whinge, Australia has similar tight laws to UK and has very little gun crime. I actually have a firearm licence and licensed rifles, which have to live locked up in safes and ammo locked in different safes, so not much use in a hurry. Any crook with a gun gets a pretty clear go, and the coppers figure it out later, but very little, and none of the mass shootings you get in the States.
TBH, there are plenty of examples of Britains who got jailed for defending themselves - here's a horrific knife example where a guy stabbed a drugged up crazed man who broke into his house covered in blood after smashing up several other houses on the street, attacked his girlfriend and then him and his friends and couldn't be stopped until the guy stabbed him 4 times, 3 time totally superficially, so once in effect really. He got 5 years for defending himself as it was ruled excessive force! :
Five years in prison for acting in self-defence
I'm pretty sure in some US states, if someone is inside your house or sometimes your garden they can be shot on sight. I remember watching one on cops where a man tried to break into a house with the homeowner inside and the homeowner shot him dead through the patio door as he tried to force it. The police came, he wasn't even arrested. To my mind that is how it should be. If it's clearly self defence, then the homeowner shouldn't be arrested.
As for gun security, you're right. That's the one thing the US gets wrong. One of the biggest reasons the UK / Aus have so little gun crime is because the background checks / requirements are so tough AND all guns have to be locked in safes at all times they're not in use. That prevents impulse killings and also these school shootings as youngsters can't steal a parents gun and take it to school / college.
I keep all my frying pans and kitchen knives right next to the front door along with some pepper spray, an umbrella and a baseball bat.
I hereby award you the honour of burglars best friend. I just hope you have some good toilet roll, the 3 ply stuff, not the 2 ply stuff to fight the (your) knife wielding burglar off with. As for the frying pan, I suggest the loo brush and a night in with some Errol Flynn movies to brush up on your fencing technique!