Senpai you can't pull knives on people in the UK. Depending on the circumstances actually just having a knife in your possession can be an offence in law.
You aren't allowed to just pull weapons on people here either. But hey, you're also not allowed to sexually assault people. 
You are allowed to have knives concealed as long as they meet a certain length.
The self defense law on it is a little tricky, you aren't allowed to pull a knife unless you're going to use it. So pulling a knife is illegal up to the point of actually stabbing them (or attempting to), as odd as it sounds because if you had no intention of stabbing then it wasn't really pulled in self defense.
Unfortunately, I have no interest in waiting until I actually need it when I could avoid being assaulted by just showing it. Where I lived the cops wouldn't show up unless it was a homicide past a certain time. I'd rather avoid confrontation, and they'd rather avoid being stabbed. It worked out for both of us quite nicely that way.
Really, out of all the situations I've had to deal with, pulling it twice is an incredibly good show of restraint in my opinion. Not that I'm "rough" by any means, I'm actually quite friendly and amiable irl. I just lived in an area where you needed to take precautions for your own safety.
But now I live in a safer area where carrying a knife is no longer necessary. I carry when I hike for utility purposes. The worst I treatment I face now is a "Oh excuse me, but I need to get through" or "Do you have a moment to hear about our Savior?". 