UNITED KINGDOM- Legally classified as an offensive weapon since January 1989, the Butterfly knife Butterfly knife are legal to possess. However, carrying on in public is an offense in the UK under the Prevention of Crime Act of 1953. Importing, Sale of, lending, giving or hiring is prohibited by the Criminal Justice Act of 1988 as amended by the Offensive Weapons Act of 1996. Any Butterfly knife imported are liable to be seized and prosecution may follow with the exception of knives of this type that are over 100 years old that are classified as antiques.