Thousands of people are using a scam to secure residency for non-EU family members in the UK by creating false "lives" in Ireland, it has been reported.
Fraudsters are believed to be making millions of pounds by helping close relatives of UK nationals from outside the European Economic Area (EEA) to create the fake histories and circumvent immigration restrictions.
The scam exploits laws that allow residency to be decided on European free-movement rules, rather than UK immigration laws, if a spouse of a British citizen comes to Britain after working in another EEA country.
The British government warned it was a "growing industry" and anyone caught attempting to cheat the system could be banned for 10 years.
An investigation by the BBC's File On 4 has found immigration advisers, lawyers and accountants were involved, with people paying up to £25,000 each to secure the required paperwork.
Det Supt Stephen Courage, from the Garda National Immigration Bureau, explained how the fraudsters were making the "staggering" profits.
"The facilitator will quite often set up a company, of which you will either be an owner or a director," he told the BBC.
"They will also create a work history for you.
"They will create payslips, they will open bank accounts, and also pay nominal tax so when the immigration service receives an application to exercise EU treaty rights, they will look at the paperwork and on the face of it, it will appear that you have a life in Ireland.
"The people we are coming across in our investigations are often from a professional background, whether it be in law or accounting, these are white-collar criminals.
"The profits they're making are staggering.
"We would see this as a multi-million euro enterprise."
UK immigration minister Robert Goodwill told the BBC: "There is a growing industry, fed by unscrupulous immigration agents, that seeks to exploit free movement rules to help non-EEA nationals circumvent our immigration system, creating backdoor routes into the UK.
"Last month we introduced tough new regulations which allow us to remove these individuals and ban them from re-entering the UK for 10 years."