He is among an increasing number of British homeowners arming themselves against the risk of attack from intruders.

Most have used the internet to make their illicit purchases from France and Germany. As well as stun guns, these include CS gas canisters and replica handguns, which, using materials that can be bought at any DIY store, can easily be converted into lethal weapons.

Customs officers say that they have seen a six-fold increase in the number of stun guns being seized at ports and airports. Last year, Customs intercepted 672 stun guns, which can paralyse victims with a 50,000-volt shock. Those found carrying the weapons all told officers that they wanted them for their own protection.

A Scotland Yard investigation into a French company selling arms on the internet found that many of its British customers were not underworld figures but respectable mortgage-payers from the shires. Raids on customers’ addresses took officers to stockbroker belts, gated private estates and properties costing several millions. The weaponry seized included shotguns, ammunition and automatic pistols. A number of the weapons’ owners are still under police caution while prosecutors consider their next move.

Senior police officers admitted that they were suprised at the numbers of homeowners who were contemplating taking the law into their own hands. The buyers were not only confused over what the law says about their own protection, but also did not realise that some items that are freely available and legal in France and Germany are not permitted here.

The Sussex businessman who, realising that he was in possession of an illegal weapon, did not wish to give his name, said: “I don’t consider myself a criminal. At least three homes in my neighbourhood have had intruders while the occupants were there, and I thought this would be a deterrent.”

A Scotland Yard spokesman said that police had no idea how many of the replica weapons were in circulation.

Some internet servers have blocked websites selling weapons, but police sources say specialist publications on sale in Britain carry more obscure outlets that supply weaponry legal in many European countries but banned here under the Firearms Act.

A police spokesman said: “Those homeowners we found in possession of weapons told us they purchased them online by simply typing the word ‘gun’ into a search engine.”

The Scotland Yard report came after Operation Bembridge, the first national crackdown on illegal firearms and weapons bought on the internet. Details of British buyers were obtained by the FBI after a request by the National Criminal Intelligence Service.

French police also acted against the company supplying the weaponry. In London, 11 men were arrested after raids on 18 addresses. More than 20 weapons were seized.

Illegal possession of firearms carries a minimum five-year sentence.

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