A 14-year-old boy bought a 100,000-volt stun gun over the internet, police have said.
Customs and Excise is investigating how
the stun gun, classed as a firearm in the UK, got into the country.
It is believed the teenager, from Merseyside, bought the weapon on a US-based website.
A police spokeswoman said the boy handed in the stun gun after an officer visited schools to talk about the dangers of carrying weapons.
Merseyside Police say the boy bought the weapon to defend himself after becoming involved in a fight with other boys.