Illegal working hurts good business, undercuts legal workers and creates illegal profits. It also puts illegal workers themselves at great risk. By working together with employers we can level the playing field and tackle the exploitation of vulnerable migrants. The UK Border Agency
HM Revenue and Customs has to verify a persons ID when they register as self-employed, for CIS, tax credits etc.
One of the forms of ID can be a letter from a Government department to the applicants home address. If you are a failed asylum seeker you will certainly have also a letter from a government department, namely the Home Office.
This letter will say that the subject is specifically forbidden from working or claiming benefits, as the failed asylum seeker has been denied rights to asylum.