We’re not lawyers, but we kept getting asked this question so we looked into it.
Carrying a folding pocket knife with a blade of less than 3 inches in length is legal in the UK IF the blade does NOT lock in place. However, this is context sensitive. You may well get away with carrying a small blade when camping or trekking, but if venturing to the pub after pitching tent then leave it in your pack at base.
Unless you have a very, very good reason to carry it, you shouldn’t ever leave the house with any blade longer than 3 inches which doesn’t fold up like a Swiss-army knife. Your only defence if you get caught or reported with something other than a small folding knife will be if it is a genuine need for your work (gardener, farmer), religion or specialist pastime (bakery, martial arts when carrying relevant paperwork) and you are engaged in that activity at that time. For example, I have a 3-inch locking blade on a multi tool as part of my Search & Rescue gear. I have to take it off if ever attending a fundraising or non-search event despite it being part of my ‘kit’.
The law applies to any public place – camp sites, public footpaths etc. So if you fancy taking your machete camping to cut some firewood, maybe consider taking a saw instead, since ‘lawful excuse’ is in the eyes of the police officer. If they think you’re not justified in having the knife, you’re in for a rude awakening.
A folding knife with a safety lock is NOT OK for the above every-day use. If you want to carry a knife with any sort of locking blade (even a safety lock) you need the ‘lawful reason’. Even a multitool with a locking blade is illegal when out of context of work or ‘need’.
One last note… it is perfectly legal for a shop to sell anyone over 18 a locking knife. As soon as you purchase it you are then ‘in a public place in possession of a locking knife’ and require the good reason. I’ve just read the story of a decorator who purchased a locking pocket knife as part of his shopping, was stopped in the street and searched and then jailed (source). Make sure that, if you wish to carry a knife, it folds, doesn’t lock in any way, and that you have a good reason.
Here’s what the UK Home Office have to say on the matter:
OK to carry:
Unless you’re in a place where there’s no justifiable need for a knife, i.e. a Pub, School, Cinema etc.
Not OK to carry:
Blades more than 3 inches from tip to handle
Any straight (non-folding) knife, of any length
Any locking knife (even an Opinel or Leatherman which locks), of any length blade