It is an offence to carry any sharp or bladed instrument in a public place, with the exception of a folding pocket knife where the cutting edge of the blade is 7.62 cm (3 inches) or less.
A lock knife is not a folding pocket knife and therefore it is an offence to carry around such a knife regardless of the length of the blade, if you do not have good reason. A lock knife has blades that can be locked and refolded only by pressing a button. A lock knife has a mechanism which locks the blade in position when fully extended, the blade cannot be closed without that mechanism being released. A lock knife is not an offensive weapon per se, as these knives were made with a specific purpose in mind were not intended as a weapon. However, possession of a lock knife in a public place without good reason is an offence.
Possession of a multi-tool incorporating a prohibited blade or pointed article is capable of being an offence under this section even if there are other tools on the instrument, which may be of use to a person in a public place, for example a screwdriver or a can opener. It is for the person to prove on the balance of probabilities that they have a good reason for possession.
The ban is not total, it is for the person in possession of such an instrument to prove on the balance of probabilities that they had good reason for its possession. It will have to be genuine, for example, someone back packing across the Lake District may reasonably be expected to have a knife for the preparation of meals. It will be far more difficult to justify on the streets of a city or town, but there will be occasions when someone is genuinely going to a martial arts sport or scout meeting which is easily checked.
The penalty for committing this offence is a maximum prison sentence of four years.
Be aware that some bladed articles may be deemed to be offensive weapons, for example, flick knives, daggers and butterfly knives. There is also an offence of carrying an offensive weapon in public without lawful authority or reasonable excuse. Please see Q338 for further information.