Criminals are using a legal loophole to import guns into Britain for use in street shootings and robberies, the Standard can reveal.

They are exploiting legislation allowing people to own firearms legally if the weapons are classified as “antiques”, according to police and officials.

The guns — which detectives say are lethal weapons — are brought from Europe, where they are easily and legally bought at antique arms fairs. Police say they are also being traded in the UK on the internet, with gang members receiving them in the post.

Among them are high-powered weapons such as a 1935 Browning Hi Power pistol — versions of which have been used by the British Army until recently — and the classic Webley Mark VI revolver from the First World War.

It came as police made what they said was one of their biggest ever hauls of guns in London.

Thirty firearms including assault rifles, sawn off shotguns, Uzi and a Thompson machine gun were seized from an address in E10.

A 51 year old man was arrested at the address is being held in custody, police said.

Under Home Office guidance, neither gun is classified as an antique but a legal loophole allows both to be considered as “antiques” under the law. All handguns were banned in the UK in 1996 after the Dunblane school massacre. However, the anomaly revolves around section 58 of the 1968 Firearms Act, which gives an exemption to “antique” weapons if they are considered as “curiosities or ornaments.”

Campaigners say the Act fails to define “antique” but leaves the matter to the police and courts to decide.

Detectives say there is evidence that “antique” guns have been used in shootings in London, while police in Birmingham say similar guns have been taken on at least two robberies — one involving injury to a person.

Working guns traded online are sent in the post for £300 to £400 a time.

Detectives in London are understood to be investigating several cases where individuals have arranged the purchase of antique guns for gang members.

One gang squad detective in the capital said a boy aged 17 quoted the Firearms Act to officers when he was stopped with a historical gun in east London. Police say gang members are buying guns from dealers, often with few questions asked, and then obtaining home-made ammunition from underworld armourers.

The trend has prompted law enforcement agencies to lobby the Home Office for tighter laws on the sale and possession of antique guns.

The National Ballistics Intelligence Service, which keeps a database of all guns seized by UK police forces, is calling for a series of changes with support from senior officers in Scotland Yard’s Trident gangs unit. Nabis spokesman Clive Robinson said: “Our concern is that at the moment you are entitled to walk down the street with an antique firearm capable of firing real bullets.

“Criminals are finding it difficult to acquire modern weapons so they are having to find alternative sources of supply such as antique weapons.

“We are finding criminals with a knowledge of the law. They recognise that they can carry these weapons with little or no risk of jail.”

Officials and senior police officers want new laws making it an offence for someone convicted of a serious crime to possess an antique weapon.

They also want new legislation similar to the recent Scrap Metal Act, forcing dealers to record all transactions and ensure sales cannot be made in cash.

Mr Robinson said: “Guns like these have not really changed in 100 years and we know there are hundreds and hundreds of these in the country.”

He warned that as the centenary of the First World War passes, more modern weapons such as automatic pistols will become classified as antiques and legal to own. Det Supt Gordon Allison, of the Yard’s Trident Gang Crime Command, said: “We are not talking about converted weapons — these guns are capable of firing live ammunition.”

Other examples of “antique” guns include the 1920s Dutch revolver carried by the killers of Drummer Lee Rigby.