Trust me, if BB don't seem to be too interested in a legal issue concerning knives then it's probably not worth worrying about!
There's a knife law thread on this forum for you to look at if you need information but, in a nutshell, if your blade is longer than 3 inches or has a lockable or fixed blade then you're gonna need a good reason to carry it.
Walking across mountains, moors and forests with a pack full of kit and a map case flapping around in the wind will not mark you out as a criminal and as long as you're not being highly irresposible you're not likely to even be looked at by a copper.
As far as I know this knife amnesty is the same as all the others before it - you are not legally required to hand in any knife and the law has not changed regarding ownership or use of knives.
I may be wrong though and if anyone knows any different then please correct me.
''It is poor manners to ask someone for the loan of his axe.
It is worse to use it without permission.''
- Mors Kochanski