Stun guns 20 times more powerful than the Tasers used by police are being illegally shipped into the UK.
A BBC documentary has found that in the past three years 500 stun guns have been seized by the Metropolitan Police in London and that they are becoming the weapons of choice for inner city criminal gangs.
The documentary also revealed that a gun with a charge of one million volts can be bought by mail order for as little as £60 and shipped to the UK.
The BBC Inside Out programme ordered two devices, both of which made it through customs.
The Metropolitan Police force says that it has investigated more than 200 cases in the capital involving the weapons - but admits that the figures could be far higher. Possessing a stun gun can carry a maximum jail sentence of 10 years in the UK.
One former gang member also claims that the weapons are increasingly being used by teenage gangs because of the crackdown on gun crime
The UK Border Force (UKBF) has insisted it is tackling the problem.
The BBC said the weapons were purchased without any questions about age or criminal status from a German website. The guns arrived within days and were accompanied by a can of free, and also illegal, pepperspray.
Eran Bauer, of Civil Defence Supply - which supplies Tasers to the UK police - described it as "one heck of a brute".
He told the BBC after seeing it fired he said: "That's lightning - horrendous tool.
"I don't believe you managed to get one of these. That is seriously dangerous."
BBC reporter Mark Jordan said there are potentially hundreds of the weapons arriving the UK each week. He claims one officer said there could be as many as 10,000 Tasers in the hands of criminals.
MP Keith Vaz, the chairman of the Home Affairs select committee, told the Inside Out programme: “I’m absolutely shocked that there are present on the streets of London and other cities these stun guns and Tasers that are more powerful than the weapons that are being used by our police.
“How is it possible for someone to be able to go online and get a gun into this country through what we are told is one of the most sophisticated borders in the world? Clearly it’s important that we take action to find out what’s gone wrong and I clearly intend to raise the matter with the head of The Border Agency and the Home Secretary when she next appears before the Select Committee.”
A Border Force spokesperson said: 'Stun guns are prohibited under the Firearms Act and anyone possessing one faces a 10 year jail sentence.
'Border Force, Revenue and Customs and police work together to target the importation of any illegal weapons, seizing them at the border and targeting those who seek to bring weapons into the country.'