As has been said, all SAK are perfectly legal to carry around without good reason but still keep your wits about you. If you get caught in a scuffle the police are bound to be a bit suspicious at you carrying a knife and might try and argue that it was an offensive weapon. Don't carry it in places where you really aren't likely to need it - big cities I usually give it a miss and check the policy of your place of work as many don't allow you to carry knives. One final piece of advice: If the police want to confiscate the knife off you then don't stop them and don't argue the law with them in the street; Ask them where the local station is and head down there afterwards to argue your case and get the knife back after explaining why it was fine for you to be carrying it.
But basically, if you don't get in fights and don't do anything to make the police suspicious enough to stop and search you or make them think you would use the knife illegally then you won't have any problems; I carry a SAK almost everywhere I go except when going to college and I've never had a problem.