The recent wave of murder and assault with knives in Europe is horrifying to Europeans but a little difficult to take seriously from an American perspective. "In Berlin on Saturday, a knife-wielding teenager ran amok among people attending celebrations to mark the opening of a new railway station. Some 28 people were injured in the incident." Yes, very bad, but not exactly on scale with, say, Columbine. If my choice is between a knife-wielding teenager and a gun (or bomb)-wielding one, I'll take my chances on the blade.
In particular, the British knife amnesty is really confusing. I understand how U.S. firearm amnesties work -- you have a gun that may not be wholly legally yours and is not registered with the proper authorities. Instead of waiting for the NRA to be right and the government to kick down your door and find the gun, you take it down to the police station and get some cash or perhaps a toy. But why would anyone turn in his knife, unless he'd committed a crime with it and wanted to get rid of it anonymously? As far as I know, one can buy a knife in the UK or even bring one's cooking knife set from overseas, provided that it's not in the carry-on luggage. The knives used for crime don't seem to be particularly fancy: "The latest litany follows the death of Special police constable Nisha Patel-Nasri, who died when she was stabbed with her own kitchen knife on her doorstep in northwest London on May 11."
I'm not a fan of guns, partly because they have a rather limited set of uses. They are for shooting people and things, and while the shooting may be done for important purposes (self-protection, animal population control, sustenance), I am not convinced that these outweigh the negative consequences of the enormous number of firearms in the United States. Knives, however, are decidedly more versatile. Nearly every person will use a sharp knife at some point for wholly peaceful purposes, and Swiss Army knives are legitimately designed to be carried in a pocket so one can perform nonviolent tasks such as opening a box with them. Metropolitan Police Commissioner Ian Blair's recommendation, of a mandatory prison sentence for carrying a concealed blade, therefore seems a bit impractical.