The boom in executive-style war games, such as paintballing, is providing criminals with a ready supply of guns that are being converted into lethal weapons, a confidential Scotland Yard report says.
The reports also highlights a small Derringer blank-firing pistol, which police say is easy to convert into a deadly weapon and has become particularly popular with the girlfriends of drug dealers because it is easy to hide.
The compact Kimar Derringer blank-firing pistol is "notoriously simply to convert," says the report.
"Derringers are particularly popular with female companions of 'Yardies' [Jamaican crack cocaine dealers] because of the ease of concealment."
To convert the Italian-made guns, a hole is drilled through the blocked barrel. "The whole process takes less than two hours and would cost usually around £50 in a backstreet workshop," the report notes.
The Metropolitan Police study concludes that one of the main factors behind the current spate of shootings is the conversion of replica and air weapons into pistols that fire live ammunition.
Gun crime in England and Wales has risen to record levels, with 10,250 incidents, including 80 murders, involving firearms in the year up to April.
The restricted internal report, "Tackling Gun Crime in London", was written earlier this year by officers from the Metropolitan Police's specialist crime directorate.
The report warns: "In recent years there has been an extraordinary improvement in the quality of the replica weapons available on the British firearms market, and, in particular, a rapid growth in 'air-soft', black-powder, CO2 or 'blank-firer' replica weap-ons, directed in particular at war games enthusiasts and at other 'sport shooters'.
"Replica weapons can be purchased directly from sports goods stores, gunsmiths or from Army and Navy-style market stalls, in stores dedicated to the pursuit of war game equipment and clothing, mail order advertisements that appear in gun magazines or they can be obtained from suppliers who advertise over the internet."
The air weapons are converted by drilling out the gas cartridge, which is used like a sleeve for the live round of ammunition to fit into. The airguns can be sold to anyone over 17 because they are not classified as firearms.
The Met believes most gun incidents now involve converted weapons.
The study says that the number of firearms incidents in London increased by about 700 to 5,410 in 2002. The most recent figures show that the Met secured a drop of about 14 per cent in gun crimes in the year to September.
Recent action against armourers includes a raid on a suspected mini arms factory in south-east London last Thursday. Police seized about 60 gas-fired, replica firearms that were being converted to fire live ammunition.
The firearms assessment warns: "A big threat facing the Metropolitan Police Service at present is the availability and use of converted replica weapons.
"The legal replica market of air weapons and blank firers is growing in the UK and there is no control system in place. Weapons are sold through a variety of means including sports shops, backstreet stores, magazines, mail order and the internet."