Deadly knives that "explode" in their victims

Police fear gangs may arm themselves with deadly knives that "explode" in their victims.

American-made hunters' Wasp knives, costing £200, are designed to kill sharks and bears by thrusting a frozen compressed gas ball into them. It expands to the size of a basketball, instantly freezing surrounding organs.

A police source said: "This knife will almost certainly kill. It's only a matter of time before one of them is used."