At the risk of being downvoted into oblivion: No guns.
In the US, if you're going to assault someone, they may well be packing. It makes you think twice. But in the UK, you know they're not (with close to certainty), so the only question is whether you're tougher than them.
Scotland used to be the most violent nation in the developed world according to the UN.
https://news.ycombinator.com/item?id=6415504
http://www.independent.co.uk/news/uk/crime/the-streets-of-sc...
http://www.theguardian.com/uk/2004/apr/11/ukcrime.lornamarti...
Things have got better over the last five years. It's still pretty bad. http://www.bbc.co.uk/news/uk-scotland-glasgow-west-22276018