The laws about buying and carrying a knife depend on the type of knife, your age and your circumstances.

Basic laws on knives

It is illegal to:

sell a knife of any kind (including cutlery and kitchen knives) to anyone under 18
carry a knife in public without good reason – unless it’s a knife with a folding blade 3 inches long (7.62 cm) or less, eg a Swiss Army knife
carry, buy or sell any type of banned knife (the list of banned knives is below)
use any knife in a threatening way (even a legal knife, such as a Swiss Army knife)
Lock knives (knives with blades that can be locked when unfolded) are not folding knives, and are illegal to carry in public.
The maximum penalty for an adult carrying a knife is 4 years in prison and a fine of £5,000.

Good reasons for carrying a knife:

Examples of good reasons to carry a knife in public can include:

taking knives you use at work to and from work
you’re taking knives to a gallery or museum to be exhibited
the knife is going to be used for theatre, film, television  historical reenactment or religious purposes (eg the kirpan some Sikhs carry)
A court will decide if you’ve got a good reason to carry a knife if you’re charged with carrying it illegally.

Knives that are illegal

There is a complete ban on the sale of some knives:

flick knives (also called ‘switchblades’ or ‘automatic knives’) – where the blade is hidden inside the handle and shoots out when a button is pressed
butterfly knives – where the blade is hidden inside a handle that splits in two around it, like wings; the handles swing around the blade to open or close it
disguised knives – eg where the blade is hidden inside a belt buckle or fake mobile phone
gravity knives
sword-sticks
samurai swords (with some exceptions, including antiques and swords made to traditional methods before 1954)
hand or foot-claws
push daggers
hollow kubotan (cylinder-shaped keychain) holding spikes
shuriken (also known as ‘death stars’ or ‘throwing stars’)
kusari-gama (sickle attached to a rope, cord or wire)
kyoketsu-shoge (hook-knife attached to a rope, cord or wire)
kusari (weight attached to a rope, cord or wire)
 

This is not a complete list of banned knives. Contact your local police to check if a knife is illegal or not.