Don't do this unless you want your full details held on police record.
Just wrap it up and throw it in the bin.
No chav would get it's Burberry dirty rummaging in land fill to find a knife.
I've had a similar situation, found a baggie full of white powder on the bus and decided to be a good citizen and hand it into my local nick, ended up getting questioned, name and address taken and treat like a dealer. All because I didn't want some kid picking it up and getting poisoned. Bend it over in a vice or kill the edge of you want but handing it in might cause problems