I don't need to carry a knife in a pubic place, indeed you put yourself at more harm carrying one, as it can be taken off you and used against you.
As for a knife crime happens every 52 minutes, that includes domestic disputes, and I am sure that of the couple of dozen people stabbed in the UK every day that a good deal are domestics or are actually stabbed by someone they know.
The police have also launched searches at transport interchanges, street stop and searches, you can be searched in places such as shopping malls, there are searches on the doors at nightclubs, teachers now have access to knife scanners, and if you ever used a knife the chances are it would be recorded on CCTV .
You are better off trying to keep away from areas you don't feel comfortable in or people that might cause conflict in the first place, than to go out with a blade.
http://cms.met.police.uk/news/major_operational_announcements/more_than_500_knives_seized_in_blunt_ii
http://news.bbc.co.uk/1/hi/england/7422516.stm
http://www.guardian.co.uk/uk/2008/jan/20/politics.pupilbehaviour
http://www.guardian.co.uk/uk/2008/feb/19/ukcrime
http://news.bbc.co.uk/1/hi/wales/5113194.stm