Those required to re-sit the test will be issued with vouchers to cover the cost at the CITB's expense.
Systematic cheating and fraud was uncovered by a BBC Newsnight report last month. Future Training 4 Jobs in Ilford, Training Xpress Limited in Colindale and Wep HSE in Ealing were all exposed by hidden camera filming.
The Construction Skills Certification Scheme (CSCS) has been left with a significant damage repair exercise. Willmott Dixon health, safety and environmental manager Alistair Donaghey told the BBC: "I'll never trust the scheme again."
However, the CITB said that it already knew that the test centres exposed were cheating before the Newsnight report. Five testing centres have been closed and a further eight are under investigation. CCTV is also being installed in all test centres and spot checks are being stepped up.
CITB director Carl Rhymer, who is responsible for ‘delivery and customer engagement’ said that the ‘vast majority’ of tests had been confirmed as legitimate following a review but it would ‘require 6,000 individuals to be retested... to eliminate any doubt’.
Mr Rhymer said: “We know card fraud is a serious problem for the UK construction industry and we are tackling this head-on. We were actively investigating and had shut down five internet testing centres before the Newsnight programme was broadcast. Three of these centres were featured in the programme.
“Whilst it is impossible to eliminate fraud completely, we are working hard with CSCS and the Police to crack down on fraud and we are accelerating existing plans to install mandatory CCTV in all testing centres. We’ve also increased the number of spot checks on centres, to act as a deterrent."
He added: “We have reviewed all test results and evidence indicates that the vast majority of the tests are legitimate.Following analysis of how the test was answered, using known testing patterns and geographical factors, we will require 6,000 individuals to be retested. Many of these are expected to be legitimate, but this is to eliminate any doubt.
“CITB is advising employers that they do not need to take any action, unless a CSCS card has been revoked. If employers have any concerns, they can contact 0344 994 4053, a dedicated helpline that we have set up.
“All retests will be taken at centres operated by Pearson VUE. Individuals retesting will need to register within a month and have completed the test within three months. CITB will issue vouchers to cover the cost of retesting.
“Safety on site is paramount, but we cannot do it alone. We are calling on all employers to check the validity of CSCS cards by using the Smart technology contained within the card. Alternatively you can use the ‘CSCS Card Checker’ or citb.co.uk/cardcheck to make sure that all revoked cards or achievements are picked up and unqualified individuals are prevented from working onsite.
“Our intelligence suggests that organised fraud is focused and accounts for very small proportion of the achievements issued legitimately every day. Where possible, we always work with law enforcement to prosecute those engaging in fraudulent activity.”