Seven construction workers were detained on suspicion of working in Britain illegally during unannounced counter-fraud visits by CITB, police and the Home Office.
Three other men involved in the delivery of CITB tests were also arrested for Fraud Act offences.
CITB audits of health, safety and environment (HS&E) test centres in Cheshire, Essex and London in recent weeks found staff giving the answers to candidates, some of whom are believed to be working in the country illegally.
At the Cheshire centre a staff member admitted helping candidates choose correct answers, while a considerable amount of cash was found without a plausible explanation.
A candidate was also detained and bailed on suspicion of being in the country illegally. In Essex, staff members admitted being supplied with a large number of candidates, many of whom the administrators were paid to give the right answers to during the test.
Candidates admitted paying up to £500 to take the £21 HS&E test.Six candidates were suspected of being in the country illegally and were detained, while the centre was suspended from carrying out further tests.
In London, the Metropolitan Police, supported by CITB investigators, arrested a man suspected of facilitating corrupt tests for other candidates. A quantity of fake documentation and card making equipment was seized from a number of locations. The man has been released under investigation pending further enquiries.
CITB will now review just over 2,500 tests conducted by these centres in the past year and then decide whether or not to revoke them.
Ian Sidney, CITB Fraud Manager, said: “CITB has considerable experience in auditing test centres all over the country, and works with the Home Office, police and other law enforcement agencies where necessary on behalf of the construction industry to ensure a safe working environment for all.
"If anyone has information about fraudulent testing within construction they can contact CITB anonymously on email@example.com”
Organised crime can earn £50,000 per week through illegal immigration and modern slavery networks, with far less risk than drug or gun crime. For example, during an unrelated joint visit by police with CITB earlier this year, half a million pounds in assets were seized.
Some workers arrive in the UK legally but are duped into thinking that the cards or qualifications they require are impossible to obtain and that expensive counterfeit versions are their only option. There are also those who are trafficked illegally, with fraudulent cards in a package awaiting them on arrival, and they are made to believe they remain in debt indefinitely to a gangmaster.
So far in 2019 CITB has terminated 17 test centres involved in delivery of fraudulent tests or CITB qualifications.
CITB supports the police and the Home Office concerning fraudulent card use, which has been found to be involved in cases of illegal immigration and modern slavery; CITB recently assisted during an operation at Battersea Power Station.