By David Bamber and Alex Pasternack
Illegal stun guns, which are being used by muggers and robbers to incapacitate their victims for up to an hour, are being sold openly on the internet for less than £20.
Criminals use the guns, officially classified as firearms, because they do not cause permanent damage and so their use is hard to prove in court.
The Telegraph has discovered, however, that the guns are widely available on the internet. One site boasts: "We can deliver all the goods on our website anywhere in the world - it's our speciality.
"However, some of the items may be slightly or very illegal to import or own in your country or state. So please check with your authorities before ordering (if you are bothered, that is)."
The internet auction site eBay.co.uk is offering stun guns for sale from various countries for delivery in Britain. One advertisement displays an 80,000-volt stun gun with an opening bid of as little as £13.82. Another advert boasts that stun guns can kill dogs and says that they are available for less than £20.
Stun guns are illegal under the 2001 Police and Criminal Evidence Act but police believe that there are as many as 10,000 of them in Britain.
Last November, a gang in Daventry, Northants, used a stun gun to attack a lorry driver and steal his load of £250,000 worth of alcohol.
Increasing numbers of the guns are being intercepted in the post and recovered during police searches for drugs.
The guns can, in rare cases, be lethal. In 1996, a postman died in Bradford after being attacked with a stun gun.
One website explains how the guns work: "The stun gun does not rely on pain for results. The energy stored in the gun is transferred into the muscles.
"This instantly depletes the blood sugar by converting it to lactic acid. In short, he is unable to produce energy for his muscles, and his body is unable to function properly."
A report from the all-party parliamentary group on gun crime last year recommended a review of Customs procedures for clearing parcels brought into Britain through private companies.
A Customs and Excise spokesman said: "Well over 90 per cent of all weapons smuggled into this country come via mail order. We are aware stun guns are coming into Britain in increasing numbers.
"It is causing concern. They are dangerous and potentially deadly if a child, or person with a heart problem, was attacked with one."
While the possession of stun guns and CS sprays is punishable with a maximum jail sentence of 10 years and an unlimited fine, most cases are treated less seriously. Those caught attempting to bring the weapons into the country face having them confiscated but further action is rarely taken.
A spokesman for eBay, which is American-owned, said: "We do not sell, or condone the selling of, illegal weapons and we will investigate if people are getting around our rules."
A Home Office spokesman said: "Stun guns are already illegal in Britain and we are very concerned that they are so easily available over the internet."