A point I think is worth making...
...we would be wise not to draw too clear a distinction between knives costing hundreds of pounds and cheaper ones.
It would be just as bad (possibly evn worse) if those of us who have top flight knives (be they an F1, a Woodlore, or something made my any of the myriad cutlers we get our sharps from) were allowed to carry them, and others who had the exact same use, justification and motivation for carrying theirs were denied that right because they use a Frost's knife that only cost them £10.
The price isn't
really the issue here.
I think it should be an issue when it comes to the recent Trading Standards actions against or discussion with (depends on your point of view) custom cutlers in the Sheffield area (and others). But when it comes to the knives we carry on a daily basis it's a different matter.
Chinkapin - I couldn't agree more.
I really do like the American view of these matters.

Maybe some day we'll play catch-up over here (ha! right!)
Sapper - if you want to read all the specifics you'll have to get into reading case law.
If you just read the law as it is written and followed it both to the letter, and in the spirit it was written, you would actually be guilty of a crime.
For example, the sub 3" non-locking folder thing is not in the statute, but is as a result of case law. Under the original wording (and intent) there was nothing to make locking folders illegal for "just because" carry.
As for the car point, in part it's just "well thought out legislation" - in part it is a symptom of a country that treats everyone as if they are a criminal waiting to happen.
If you have a filleting knife in your car and you're not going to or from fishing, it could (would?) be seen as if you had it in the car for other reasons.
Think of the stories of people being stabbed in "road rage" incidents - that's the sort of thing they probably had in mind. The fact most of that is with screwdrivers and kitchen knives is neither here nor there.
As I understand it, your car is a public place because it is in public. If you're out and about with your knife in a backpack, it's still in public. Ditto with a knife in your car. If you're out and about with a knife, on your person, in a bag or in your car, you're in public with a knife.
I'm not sure if that's the logic behind it, but it makes sense and, I think, makes the whole thing a touch easier to understand.
Not that I think it is sensible - it should be clear from my other posts that I don't - but there you have it.