On your person

[bigpaul]

A lot of people mentioning lock knives.
Lock knives are not legal pocket knives. You need a "good reason" to carry one.
A non-locking knive with a blade not more than three inches is legal to carry without a reason.

A good reason is job related, carrying it becuase your job (or recreation) needs it is only acceptable if you are on the way to or from said job/recreation. Calling into the shops on your way home with a lock knife is illegal.
Carying a lock knife in work if you can't justify having a lock knife in work is illegal.

got to find mine first- its not obvious on first glance!