Good Reason to Carry a Knife: What UK Courts Accept

Good reason to carry a knife means proving one of a small set of accepted purposes applied at the time. It is not a general excuse a person can construct after being stopped.

Section 139(4) of the Criminal Justice Act 1988 makes good reason or lawful authority a defence the person carrying the knife must prove. Section 139(5) names three examples: use at work, religious reasons and national costume ^[1]. Gov.uk repeats the same three categories directly. It adds the Sikh kirpan by name under religious reasons ^[3].

This page sets out the statutory examples, the rejected reasons, and how the burden of proof works.

Work, religious observance and national costume are the statutory examples explained below, including the kirpan and sgian-dubh. The guide also sets out the wording used in Scotland and Northern Ireland, and why general self-defence and forgetting a knife do not qualify on their own.

What are the main accepted good reasons?

Use at work, religious reasons and national costume. These are the three examples written into section 139(5). The list is not closed. Section 139(4) allows any good reason the person can prove ^[1].

Reason	Typical example	Applies to
Work	Chef’s knife carried to a catering job, tradesperson’s locking multitool	Any knife genuinely needed for the specific job
Religious reasons	Sikh kirpan	Genuine religious observance
National costume	Scottish sgian-dubh	Worn as part of the relevant traditional dress

Each reason has to match the specific knife, the specific situation and the specific person. A chef’s knife carried to work meets the test. The same knife carried on a day off does not meet the test if no work reason is attached.

Can you carry a knife for work?

Yes, if the knife is genuinely needed for the job and is being carried in connection with it. This is the most commonly used good-reason category. It covers trades from catering to construction to agriculture.

A locking knife or a blade over 3 inches carried by a chef between home and a kitchen fits within the work example named in both the statute and gov.uk guidance ^[3]. The same applies to a tradesperson who needs it on site. The reason has to relate to the actual work being done. CPS guidance says a work reason does not apply automatically. The possession must be reasonable. There must also be an immediate connection between the knife and the work ^[4]. A knife found in a car glovebox on a Saturday weakened the defence even though the owner was a tradesperson, in Garry v Crown Prosecution Service [2019] EWHC 636 (Admin). He was not working that day ^[4].

Can you carry a kirpan for religious reasons?

Yes. Carrying a kirpan connected to Sikh religious observance is an accepted good reason. gov.uk names the kirpan specifically as an example under religious reasons for carrying a knife ^[3].

The exemption is tied to the religious purpose itself. It is not tied to any blade carried under that label. A kirpan carried and worn in the manner associated with genuine Sikh observance sits within the exemption. This does not create a general exemption for any blade a person chooses to describe as having religious significance.

Can you carry a sgian-dubh as national costume?

Yes, when worn as part of Scottish national dress. Most commonly this means Highland dress with a kilt. The national-costume example named in section 139(5) and repeated by gov.uk covers this specific traditional use ^[1].

A sgian-dubh worn tucked into a kilt hose as part of formal or ceremonial Highland dress fits the exemption. The same small blade carried loose in a pocket with no connection to wearing national costume does not automatically inherit the same protection. The exemption is tied to the dress. It is not tied to the object alone.

Is self-defence a good reason to carry a knife?

No. Carrying a knife in case you need to defend yourself is not a good reason or reasonable excuse, even where the threat you fear is genuine. CPS guidance sets out the rule plainly. It is applied strictly.

The Crown Prosecution Service states that carrying an offensive weapon in public “merely because of the possibility of a constant or enduring threat (even where genuine)” does not amount to self-defence or a reasonable excuse ^[4]. The only exception it records is narrow. Possession may exceptionally be reasonable where a person anticipates an imminent and specific attack. This must be closely connected in time and purpose to that immediate threat. This cites Evans v Hughes (1972) 56 Cr App R 813 ^[4]. That exception does not cover carrying a knife day to day because an area feels unsafe. The safe and lawful response to any threat is not to carry a knife. Call 999 in an emergency. Call 101 otherwise.

How is the defence worded in Scotland and Northern Ireland?

In Scotland the defence is “reasonable excuse or lawful authority”, not “good reason”. In Northern Ireland section 139 applies with the same good-reason wording as in England and Wales. The practical examples are the same in all three.

Section 49(4) of the Criminal Law (Consolidation) (Scotland) Act 1995 allows a person to show a reasonable excuse or lawful authority for having the article in a public place. Section 49(5) repeats the same three examples: use at work, religious reasons and national costume ^[5]. Section 172 of the Criminal Justice Act 1988 extends section 139 to Northern Ireland ^[6]. The Northern Ireland text keeps the “good reason or lawful authority” wording and the same section 139(5) examples ^[1].

Is forgetting a knife is in your bag a good reason?

No. Not on its own. The Crown Prosecution Service treats forgetfulness alone as insufficient, regardless of whether the claim is truthful ^[4].

What can matter is the fuller sequence of events. This includes how the knife came to be there in the first place. A legitimate work use is one such reason. It also includes what the person did once they realised it was there. Simply asserting forgetfulness is not treated as a defence in itself. This is true even with no supporting circumstances.

Does a good reason cover the whole journey, or just the task itself?

It has to cover the carrying, not only the moment the knife is used. Travelling to and from the specific job, event or activity that creates the good reason is generally treated as part of that reason, provided the route and timing are consistent with the stated purpose.

A tradesperson carrying a locking knife directly between home and a job site is in a stronger position than someone carrying the same knife on an unrelated errand later the same day. The reason has to remain live and connected to the actual carrying. It cannot act as a one-off explanation that covers unrelated carrying at other times.

Does the good reason have to be proved on the spot?

Not necessarily at the roadside. The proof is tested in court if the matter is prosecuted. Section 139(4) places the burden of proving good reason or lawful authority on the person carrying the knife. That proof is tested at trial if the case proceeds that far ^[1].

Being able to explain the reason clearly and consistently at the time of a police stop makes an eventual court case less likely and is good practice. Examples include naming the specific job or event. The legal defence itself is proved as a matter of evidence though, not simply asserted in the moment.

Does the same good-reason rule apply on school premises?

Yes, for articles within section 139A’s scope. It applies the same good reason or lawful authority defence on school or further education premises to articles caught by section 139 and to offensive weapons. This includes work, education, religious reasons and national costume ^[2]. A folding pocketknife exempt from section 139 is not caught by section 139A merely because it is on school premises, although a school can ban it under its own rules.

Anyone carrying a knife onto school premises for a genuine educational or work purpose needs to be able to show that specific connection. Examples include a food-technology lesson or estate maintenance work. This works the same way as the general public-place offence.

This is legal information. It is not legal advice. Get advice from a solicitor or Citizens Advice for a specific situation.