It is important to keep your Unique Tax Reference Number (UTR) confidential. There are no photocards to prove identity in the CIS system, so it is possible for an unscrupulous individual to ‘borrow’ your UTR to obtain work and then leave you with the tax bill. This may be done with the consent of (or even pressure from) the main contractor.
Where there are individuals with similar names this is particularly a risk. The victim need not even be working in construction. Students, shop workers etc can all be at risk. All that is required is that someone borrows your UTR and uses it to get work as a subcontractor in construction.
The unfortunate victim may not find out for a number of years. Often this will happen when a large tax demand arrives and it becomes clear that someone else has been submitting tax returns in your name. By this stage HMRC may already have a court judgment for the debt. It can be a difficult job to sort it out.