Complex sentence: It is legal to buy an Opinel in the United Kingdom but (with the exception of the smaller knives with a blade length of less than 3 inches, and without a locking mechanism), it is illegal to carry one in public without good reason.
Split into simpler sentences: It is legal to buy an Opinel in the United Kingdom. However, with the exception of the smaller models with a blade length of less than 3 inches and without a locking mechanism, it is illegal to carry one in public without good reason.