i am not a lawyer but two factors that enter into it are circumstances and intent if you are a chef heading to your first day of work and police stop you with a securely tied up roll of kitchen knives in your bag then you have a reasonable and lawful purpose to be carrying knives if however you are heading out to the pub at pm on a friday and you have a knife in your coat pocket then that is an entirely different story same thing with screwdrivers and other potentially offensive weapons carrying a stick of wood home from the garden centre is different to taking a baseball bat to a nightclub or being arrested with one in your hand after a fight and the law recognises that