Houses are usually full of perfectly good weapons, anyway. Knives, for instance. Or anything sufficiently heavy will do sufficient damage - lamps, toasters, kettles, irons... And in spite of what urban legend might have you think, the principle of "the best defence is a good offence" is perfectly legal. If you think you're at risk, you're entitled to take any reasonable measures in self-defence, including hitting hard and hitting first.
The only caveat is that you do have to be defending yourself. The reason Tony Martin was jailed was not that he shot and killed a burglar, but that he shot and killed the burglar when the burglar was already running away. More recently, a man stabbed and killed a burglar with no action taken. (It was correctly referred to the CPS for them to decide whether it was self-defence, and they decided it was.)
It's also worth pointing out that Tony Martin didn't Have that shotgun legally. So how much use do you think any extra laws would have been? If your answer was "f**k all", congratulations.
And rewinding to Dunblane, it's also worth noting that all *that* guy's guns *were* held legally, bcos the police were utterly incompetent at following up on firearms licenses. If they had done their job, they would have found out that his doctor knew he was a raving nutter.