Generally the rule of thumb here is you can carry a penknife/multitool without 'good reason' (other than it's useful) with a blade not exceeding 3 inches in length and which does not lock - leathermans and penknives can fall into this category. But this is subjective to how you might be 'using' it and the zealousness of the officer present.
Everything else you have to have 'good reason' for otherwise it's trouble if you get stopped with it.
But then again, having a screwdriver in your car door pocket could be seen as carrying an offensive weapon, or say a hatchet in your car boot and you're not using it for work or going some place to use it, like camping etc.
Fixed blades/locking blades and blades over 3" are verboten! unless you can prove reason to have it. Needless to say, so are flick/butterfly/fist knives as, apart for 'collectors', their only use is viewed as offensive.
Where I go hiking, I don't tend to see anyone about, but my other tools stay in the rucksack, unless I have to use them, all the same. Different if I'm camping in the usual places. I don't go waving them about, so the likelihood of me getting searched is minimal. And given that I have spare clothes/food & water/fire-lighting kit/canteen/waterproofs/tarp and other stuff in the pack, it's not like having a saw and a fixed blade knife is for use in anything other than mooching about in the great outdoors.
Most of the time the cops are interested in the chav with his small cheap kitchen knife shoved down his trousers, in town on a friday night. If you don't look the type of troublemaker it would be unlikely you'd be stopped in the first instance and given consideration for your reason to carry such an item, in the second.
On balance, I'd rather have it away on my toes, than use any of my knives as a weapon - it's just not how I see them at all and never has been.
However, there has been somewhat of a knee-jerk reaction regarding the laws about knives/firearms and anything else the nanny state thinks might possibly be dangerous, mainly due to some high media profile cases involving idiots and nutters, who obviously make up the vast majority of the population here... if you believe the papers
