To be honest I don’t think calling national emergency over this would get very far, what immediate action are the general public (who aren’t carrying knives themselves) supposed to take? If anything, I think unnecessarily calling a national emergency under these circumstances would actually lead to a national emergency as you’ll get people being more suspicious towards people, get more violent to each other in an attempt to head off a fictitious knife attack, vulnerable people who have no choice but to go about their days outside the house may be disproportionately impacted etc.
plus, you linked to this article that mentions a recent, unprovoked attack. However we know nothing else about that crime specifically. They may have been known to each other (in which case it wouldn’t warrant a national emergency). Plus, Birmingham is a rough city and a hotspot for crime. Statistically, although the crime is awful, I don’t think this sort of thing is unusual for Birmingham ie it’s likely within the tolerance of their predicted crime statistics (ie not warranting a national emergency).
I don’t disagree that gender based violence needs to be tackled but I don’t think you have really put forward any convincing points