First came the verbal warning; then the battering ram. After weeks of investigation, Operation Hypera was launched yesterday to the ear-splitting sound of splintering wood.

Inside numerous homes, immigration and police officers scoured drawers, wardrobes and cupboards looking for the new top commodity of organised criminals - fake and doctored passports.

Intelligence garnered by the UK Border Agency (UKBA) suggested that 28 people were working, or attempting to work, with false passports and documents in Edinburgh. Several of them had attempted to get jobs in the care sector, including care homes.

In the biggest operation of its kind in Scotland, more than 50 officers from the Lothian and Borders force and UKBA congregated in the police canteen to receive the day's briefing - ready to fan out across the Pilton, Drylaw and Muirhouse areas of the capital.

As marked and unmarked vans trickled out of police headquarters at Fettes in the cold, bright October light towards 27 addresses, senior officers explained why the initiative - which aimed to track down suspects under the Identity Cards Act 2006 - was so important.

They stressed links between such fake documents helping to fund serious and organised crime and the ultimate exploitation they encourage of those not legally allowed to work in the UK.

Under the legislation, it is an offence to hold fake or falsified passports and the onus is on employers to check someone's identity and right to work.

Employers must check and photocopy two pieces of identification, including a passport. Those who do not comply face civil penalties of up to £10,000.

This year across Scotland there have been 70 successful prosecutions but senior officers say this is just the tip of the iceberg.

Officers have already arrested a Liberian man with a Dutch passport, a number of Brazilians with false Portuguese documents and some Nigerians. Purloining the identities of EU citizens who speak the same language has proven particularly popular.

"This is the biggest operation of its kind," said Inspector Paul Menzies, the leading Scottish officer seconded to UKBA. "Some of those being targeted had attempted to work in the care sector.

"The legislation is still new. The problem is not new but in the past it was never really addressed.

"Ultimately, employers might think they are doing nothing wrong but counterfeit and forged documents of this kind link back to organised crime."

A number of cases have raised the profile of the legislation, including that of Marouane Bourannane, who was arrested at the Conservative party conference in Blackpool last year. He had been working as a "security officer" for Group 4 Securicor.

The Algerian national, who helped guard Gordon Brown and David Cameron, was charged with possessing a fake passport.

In May Brazilian Walter Netto, 21, was jailed for two-and-a-half years in Bristol after being found with 148 forged passports, ID cards, and driving licences. The fakes were sold to illegal immigrants to help them live and work in the UK.

According to CIFAS, the UK's fraud prevention service, identity theft has risen from 20,000 cases in 1999 to 137,000 in 2005.

The government estimates it is costing the UK £1.7bn a year, but experts have suggested the true figure is far higher.

According to a recent survey by Which? magazine, one-quarter of adults in the UK have either had their identity stolen or know someone who has fallen victim to ID fraud.

"It's a multimillion-pound industry Europe-wide," explained Sergeant Michael Burt, a Grampian officer seconded to UKBA. "London is the major distribution centre for such documents, for which people are charged between £1000 and £6000.

British passports cost the most and there is a perception that it opens a lot more doors in terms of housing and healthcare.

"We estimate that this year we have removed £150,000-worth of such documents, but this is just the tip of the iceberg.

"By its very nature this is a national security matter - not necessarily in relation to counterterrorism. It is dealt with very robustly by UKBA and can lead to custodial sentences of up to two years."

Officers stressed that Scotland - although more distant from the London distributors - was not immune to the issue. They said their concerns lie not only in cracking down on organised crime but with the exploitation of workers lured into using them.

The flats visited were, on the whole, grimy windowed, grey and small. The workers, whose families may have spent their entire life savings or gone into debt to buy the original fake passport, seem to be reaping little benefit.

"There are a minority of employers who actively create a pull factor' in encouraging persons of illegal status to come into the UK to do poorly-paid work," said Mr Burt. "One problem lies in the fact that employers may be shown a passport which is fake but they have not been trained in how to identify forgeries.

"They have no proper protection in terms of employment legislation. These people are exploited and some are living in a worse state than they were back in their own country.

"This is as significant a problem in Scotland as it is in England and Wales. We have found a lot of people coming to work illegally in London are being pushed further north because they can not get work there."