Having bladed or pointed articles in public is criminalised by s49 of the Criminal Law (Consolidation) (Scotland) Act 1995.
In terms of the concepts to be applied, there are several similarities to s47 of the same act, which covers offensive weapons, so I will repeat a fair amount of the content of that page here.
“has with him”
Note that this is not necessarily the same thing as “posseses”. In law, possession requires knowledge, whereas “has with him” only requires the presence of the object in close enough proximity to the accused.
“In Scotland it is clear…that the approach taken is that Parliament deliberately intended not to include such factors as knowledge and intent in the section and that therefore these matters are irrelevant to the initial question of whether someone has an item with him…
…The Scottish approach has been to factor in knowledge at the stage of considering whether the statutory defence is available…
…It is correct to say that a person can have an item with him without knowing of the item’s existence, at least if he ought to have been aware of it…”Lord Justice Clerk (Carloway), paragraphs 9, 10 & 11
What this means in practice is that the Crown does not need to lead evidence from which it can be inferred that the accused actually knew about the presence of the object in order to prove the charge. The question of whether the accused actually knew about it might come up in the context of “reasonable excuse” (see below), in which case the onus would be on the defence to establish it.
The words “has with him” mean that the object in question is readily available to the accused; the accused does not have to have the object in their hand or on their person.
Smith v Vannet [1998 SCCR 410]
The appellant had been convicted of a s47 offence and a s49 offence after a wooden cosh had been found under the front passenger seat of a parked car. A knife was found under the driver’s side floor mat. The appellant had been standing around six feet away from the car, with its keys in his pocket.
He appealled on the basis that he did not have the items “with him”, but his conviction was upheld on appeal.
“These weapons would have been readily available for the appellant for use…had he wished to make use of them. In our view…the sheriff was entitled to conclude that the appellant had the cosh and knife with him in the lane.”Lord Justice-General at page 413
“in a public place”
s49(7) provides that the s47(4) definition of “public place” applies to bladed or pointed articles as well as to offensive weapons. s47(4) defines a public place as anywhere that is not “domestic premises” (meaning a private dwelling, including its immediate surroundings such as its garden, garage or outhouse).
Places used by more than one dwelling (e.g. the stair of a block of flats, or a shared garden) are classed as public places according to this definition.
Schools and prisons are not included in the definition of “public place” for this offence, because there are distinct offences for having bladed or pointed articles in schools (s49A of the 1995 Act) and in prisons (s49C).
The definition of “public place” in s47(4) seems to be extremely wide, but the wording of the definition is clear.
Even in cases where the accused has been found with a bladed or pointed article in a place that any ordinary person would regard as non-public, the courts have taken the view that the accused will inevitably have carried it through a public place in order to reach the non-public place. Provided the locus is defined to include the public place, then a conviction will likely stand.
Normand v Donnelly  SLT 62
This case predates the 1995 Act, but the relevant offence here (s1(1) of the Prevention of Crime Act 1953) was worded in a very similar way to s47 of the 1995 Act.
The appellant had been convicted of having a cleaver with him in a hospital emergency department. The cleaver had been found in his pocket in a private treatment cubicle.
It was agreed that the cubicle itself was not a public place, but the Appeal Court held that the sheriff was entitled to infer that the appellant must have carried the cleaver through the (public) reception area of the emergency department in order to reach the treatment cubicle, so the conviction was upheld.
“an article to which [s49] applies”
s49(2) provides that this offence covers “any article which has a blade or is sharply pointed”.
This is, deliberately, a very wide definition. Unlike s47, there is no requirement for the article to have been made or adapted for use as a weapon, or for intent to cause injury to be proven. Anything from a pair of scissors to a spear would presumably be caught under this definition.
The only items specifically excluded from this offence are folding pocketknives if the cutting edge of the blade is no longer than three inches, so in that sense size very much matters. You might think of this as the “Swiss army knife exception”.
Per the case of McAuley v Mulholland [2003 SCCR 326], knives that have a functional locking mechanism do not count as folding pocketknives regardless of size, but if the locking mechanism is broken so that the knife can immediately fold, they may count if they are small enough.
Defence: “reasonable excuse or lawful authority for having the weapon”
The s49(4) defence is for the accused to establish, on the balance of probabilties (more likely than not).
“lawful authority” is included to protect (e.g.) soldiers from prosecution for carrying a bayonet.
As with offensive weapons, whether an excuse for carrying a bladed or pointed article is a reasonable excuse will depend on the particular facts and circumstances of the case.
McGuire v Higson[2003 SLT 890] the appellant had asked an unknown person to go into a pawn shop and buy a knife on his behalf. As soon as the knife (an 18 inch machete) was handed over, the police detained the appellant. He was convicted of a s49 offence. It was held that, if the circumstances
McGuire v Higson[2003 SLT 890]
The appellant asked an unknown person to go into a pawn shop in Glasgow City Centre and buy a knife on his behalf. Shortly after the knife (an 18 inch machete) was handed over, the police detained the appellant. He told them that he was taking the knife home. There was no evidence to contradict his position. He was convicted of a s49 offence.
His appeal was allowed and the conviction was quashed. It was held that, if the circumstances here did not amount to the statutory defence, then the effect of s49 would be to render the sale of all bladed and pointed articles as illegal, which was clearly not Parliament’s intention.
The absolute apex of “reasonable excuse” cases is Frame v Kennedy:
Two police officers approached the accused, who appeared to be a fellow officer, outside a bar in Aberdeen. He was dressed in a very similar manner to Grampian police officers, including a utility belt with two batons and a spray canister attached.
The accused immediately volunteered that he was not a police officer, but a stripper, who had been booked to perform at the bar in a few minutes.
“The police officers decided to allow him to enter the premises…Both officers were of the view that it was important to ascertain the truth or otherwise of the respondent’s stated purpose of attendance at the premises. They, accordingly, attended within the Paramount bar and saw part of his performance. Both officers were satisfied that what they had been told by the respondent was true and genuine.” [paragraph 4]
Later, after the accused had voluntarily agreed to be interviewed by the police, he admitted that the canister contained “a defence dye” which he carried in case he was assaulted, because “drunk guys get very jealous of male strippers”.
The accused was charged with possession of offensive weapons. The sheriff acquitted him after a defence submission of “no case to answer”. The Crown appealled.
The Appeal Court upheld the acquittal, holding that “the reason for the respondent having the batons on his person was to add verisimilitude to his fancy dress, and that this amounted to a reasonable excuse for having them with him at the time in question.” [paragraph 24]
Further Defences: Use at Work / Religious Reasons / National Costume
s49(5) provides for three scenarios (without prejudice to the generality of the “reasonable excuse or lawful authority” defence in s49(4)) that amount to defences to a s49 charge.
The first is that the accused had the bladed or pointed article with him for use at work, which would cover (e.g.) a gardener having a pair of garden shears.
The second is that the accused had the bladed or pointed article with him for religious reasons, such as the Sikh kirpan.
The third is that the accused had the bladed or pointed article with him as part of any national costume; the sgian dubh defence.