Scotland Yard is battling to stop criminal gangs turning London into the identity theft capital of the world.

The gangs are setting up fake-ID factories using printers bought at high street shops. The Met has shut at least 20 "factories" in the last 18 months and believes more than 30,000 fake identities are in circulation.

Police examined 12,000 of them and established they were behind a racket worth £14 million.

One £750 printer was withdrawn from sale at PC World after detectives revealed it could produce replicas of the proposed new ID card and EU driving licences.

Commander Nigel Mawer, who leads the Yard's fight against fraud, said: "There are a significant number of fake-ID factories that are producing documents for lots of different purposes.

"We have dismantled over 20 in the last 18 months and we have 27 convictions with criminals being jailed for a total of 40 years. We have also built up a database of 30,000 fake identities which are currently in circulation."

Crimes range from immigration and benefit fraud to money cons.

In some cases criminals are forging documents using the names of people whose identities have been stolen from credit reference agencies.

Many of the forgeries are "know your customer" documents such as utility bills and driving licences, which are then used to open bank accounts under false names.

Mr Mawer added: "There are people with dual identities, one real and one for committing crime." He revealed that specialist printers capable of making convincing ID documents such as EU driving licences could be bought for £750, though others cost £5,000.

The cost of equipment needed to set up ID factories is falling, making them easier to establish. Scotland Yard is working closely with manufacturers and retailers on a scheme named Project Genesius to keep printers out of the hands of criminals.

At present it is voluntary but police want the system regulated so all manufacturers abide by the code.

Detective chief inspector Nick Downing, an ID fraud expert, said PC World was planning to sell one sophisticated £750 printer but was persuaded not to stock it. He said: "These machines can manufacture any form of ID card. The frightening thing is you can go on the internet and get all the computer bits you need to set up an ID factory in 24 hours.

"This is real bespoke equipment that can manufacture passports, National Insurance cards, passport entry stamps or driving licences."

A spokesman for the Identity and Passport Service, said: "It is absolutely wrong to suggest that it is possible to copy or clone the National Identity Card."