Remeber guys that there is a difference between an offensive weapon and bladed or pointed article.
As has been said ANYTHING can be an offensive weapon depending on:
Design - is it made to be a weapon (e.g. broadawords or nunchuks)
Adapted - has an article been adapted to be a weapon (e.g. driving nails through the end of a baseball bat)
Intent - is the article being carried with the intention to be used as a weapon (e.g. carrying a piece of 2 by 4 to defend yourself from muggers)
While a bladed or pointed article is anything with a blade or point (DOH!) you have in a public place without a reasonable excuse/explination. The only exception to this is the sub 3" slipjoint folding knife
These are too totally seperate offenses!
In this case the only way that a SAK can be considered an offensive weapon is if the guy showed a clear intent to use it as a weapon.
If it helps there I started a thread on UKPoliceOnline to try and summarise and simplify the law surrounding carrying knives -
http://www.ukpoliceonline.co.uk/index.php?showtopic=41216&st=0&p=439609&#entry439609