It is important to know and understand the current laws on buying and carrying knives in the UK before venturing out anywhere with a knife, whatever its size.

The information below is taken from www.gov.uk/find-out-if-i-can-buy-or-carry-a-knife:

Knives: the laws on buying and carrying

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

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, televison, 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.

Criminal Justice Act 1988

The Criminal Justice Act 1988 mainly relates to carrying knives in public spaces, Section 139 being the most important:
(1) Subject to subsections (4) and (5) below, any person who has an article to which this section applies with him in a public place shall be guilty of an offence.
(2) Subject to subsection (3) below, this section applies to any article which has a blade or is sharply pointed except a folding pocketknife.
(3) This section applies to a folding pocketknife if the cutting edge of its blade exceeds 3 inches.
(4) It shall be a defence for a person charged with an offence under this section to prove that he had good reason or lawful authority for having the article with him in a public place.

The definition of “public place” is unsettled, but can loosely be defined as anywhere the public have a legitimate right to be whether this access is paid for or not, which could include any populated area within the United Kingdom, including one’s motor vehicle, which is defined by law as a ‘public place’ unless parked on private property. In a remote or otherwise unpopulated area, a public place could include: 1) an organised wilderness gathering or event; 2) a National Park; 3) Forestry Commission land that is held open to the public; 4) public footpaths; 5) bridleways; and 6) any area where an individual does not need to ask specific permission to walk, camp, or travel from a landowner.

The phrase “good reason or lawful authority” in Subsection 4 is intended to allow for “common sense” possession of knives, so that it is legal to carry a knife if there is a bona fide reason to do so. Subsection 5 gives some specific examples of bona fide reasons: a knife for use at work (e.g. a chef’s knife), as part of a national costume (e.g. a sgian dubh for the Scottish national costume), or for religious reasons (e.g. a Sikh Kirpan). However, even these specific statutory exceptions have proven unavailing to knife owners at times. It is important to note that that “good reason or lawful authority” exceptions may be difficult to establish for those not using a knife in the course of their trade or profession, but merely because the knife is needed in case of emergency or for occasional utility use. A person on holiday and travelling by motor vehicle in the UK might well be obliged to purchase a knife at their destination, rather than risk prosecution if one is found by the police during a routine traffic stop or checkpoint.

Although English law insists that it is the responsibility of the prosecution to provide evidence proving a crime has been committed, an individual must provide evidence to prove that they had a “good reason or lawful authority” for carrying a knife (if this is the case) upon being detained. While this may appear to be a reversal of the usual burden of proof, technically the prosecution has already proven the case (prima facie) by establishing that a knife was being carried in a public place.
As the burden of proving “good reason or lawful authority” lies with the defendant, it is likely that an individual detained and searched by the police will need to prove the following (sometimes known as the THIS list):

Has THIS person got permission; to use THIS article (knife); for THIS use; on THIS land; and by THIS land owner.

The special exception which exists in the Criminal Justice Act 1988 (Sec. 139) for folding knives (pocket knives) is another “common sense” measure accepting that some small knives are carried for general utility; however, even a folding pocket knife or multi-tool equipped with a blade of less than 3 inches (76 mm) may still be considered an offensive weapon if it has a locking blade. It is a common belief that a folding pocket knife with a blade of 3 inches (76mm) or less must have a locking blade to be considered an offensive weapon, but the wording of the Criminal Justice Act does not mention locking and the matter becomes a question as to the definition of “folding pocket knife”.

In the Crown Court appeal of Harris v. DPP (1992) and the Court of Appeal case of ‘R. v Deegan (1998) the ruling that ‘folding’ was intended to mean ‘non-locking’ was upheld. As the only higher court in England and Wales to the Court of Appeal is the Supreme Court, the only way the decision in R. v. Deegan could be overturned is by a dissenting ruling by the Supreme Court or by Act of Parliament.T’s & C’s

If in doubt leave it at home.