1) if it's from a knife amnesty, it hasn't been seized in anything other than maybe a legal standpoint. someone has willingly handed it in, and I seriously doubt it's been used in a criminal manner anyway.
2) the daily mail is fairly well known for being one of those papers who are convinced that the country is going down the toilet. they would be outraged at the lack of people carrying pocket knives, if there was a "story" that suited.
3) honestly, I'm wasn't worried untill this saturday, when I discovered that schools have been covering over pictures of knives in a GCSE Text book, I assume because it "encourages knife crime"
and fair enough, the poem/short story it is illustrating is about murder ect, but honestly, I doubt the removal of the picture is going to make a jot of difference.