In the UK Flick Knives and Gravity knives have been effectively banned since 1959. Restriction of Offensive Weapons Act 1959
The law was introduced as a result of teenagers using flick knives as a badge of manhood (Hansard) and followed similar laws introduced in the United States. It is interesting to note that the US laws were preceded by the New York Switchblade law which initially banned only what we’d call Flick Knives – i.e. knives that have a blade that is flicked into place by a spring. The suppliers of these knives were left with a stockpile of illegal knives and realised that if they removed the spring they could still sell the knives as the blade would fall out of the handle when the button is pushed and could be swung into place quickly with a bit of wrist action. The New York law was amended to include ‘gravity knives’ to address this. By the time the Federal US and UK copied the legislation, both Flick Knives and Gravity Knives were included.
Why is this interesting? The UK Border Authority have started classifying some lock knives as Gravity Knives and seizing them. At issue is whether the modern locking folder is really a gravity knife. It generally does not resemble the gravity knives addressed by the 1959 bill and indeed the Federal US has modified its legislation to exclude any knife with a bias or detent towards closed in order to distinguish them. The modified-flick-knife-turned-into-gravity-knife blade would drop out of the handle under the force of gravity alone, whilst most modern lock knives require a significant rotation to move the blade out of the handle.
The other banned knives are part of the Offensive Weapons Order to the Criminal Justice Act 1988 and are deemed offensive weapons per se i.e. possession of them in public will lead you to an offensive weapons charge.