Being from Canada I carry a leatherman surge and an opinel #8 with me everyday......in my truck I have a kit with my axe and a couple sizeable fixed blades......sorry to rub it in but I cant understand these laws.....what is the official reasoning behind it?
The first thing you need to understand is that the UK legal system is a bit different to the States (I dunno about canada). We don't have laws that grant us rights, we have laws that restrict things. These are always woolly and open to interpretation.
So it isn't 'illegal' to carry a whopping great fixed-blade knife. No sirree. You just have to have 'good reason' to have it on your possession - and that 'good reason' interpretation is up to the individual police officer. So a polite non-scruffy individual is unlikely to get in trouble for, say, carrying a 3ft sword and polearm on public transport back from a re-enactment event (as a friend was doing recently - the police were very curious about the polearm).
However, if you are a gobby rude little sod who just about spits on a police officer and you are found with a sharpened toothbrush, you will get arrested.
Why do we have these laws? Because the nasty little violent scrotes who might shoot people if they could get guns, use knives instead. Usually cheap kitchen knives.