There are legal definitions on what you can or can't carry with you eg. you can carry a knife only under a certain length, something like 7-8cm iirc
And then there are zones where you can't cary anything that could be used as a (edged/bladed) weapon at all, or you had to have it with you if it's part of work/profession etc.
So yeh.. I don't think anyone will stop you on a random street and check if you're carrying a knife on you, but you can get arrested, circumstances do matter indeed.