One of the problems of governments in general, and this one in particular, is that they constantly come up with the wrong answers.
For instance, there is a rise in knife crime—but knives are not on special offer. There aren't massive advertising campaigns urging people to get a knife. Knives are not particularly easy to get hold of (and nor particularly difficult).
In short, the availability of knives has not changed, and yet there is a rise in knife crime.
So—even leaving aside any unintended consequences—why, in the name of buggery fuck, does the government think that the solution to an increase in knife crime is to pass a law banning knives?*
* No, the government aren't passing a law to ban knives (yet) but this is the kind of response that the government undertakes.
UPDATE (an obviously needed clarification): I am not saying that there is a rise in knife crime. Or that the government are going to ban all knives. I am simply conjuring up a hypothetical but vaguely plausible scenario and outlining how the government would react. If anyone has any better scenarios, do feel free to contribute them in the comments.