When recruiting someone it is good practice to treat every applicant the same and before making your selection ensure you obtain proof of right to work for that person. It is also critical you make sure you have verified documents presented as proof, are original or valid. The fines for getting it wrong are £10,000 per illegal worker.
As long as you can demonstrate you have taken the correct steps you will then have the necessary paperwork if something goes wrong and it is subsequently determined you have employed an illegal worker.
There is a simple 3 step procedure to follow:
Step 1: Obtain original documents from given List A or List B http://www.ukba.homeoffice.gov.uk/sitecontent/documents/employersandsponsors/preventingillegalworking/currentguidanceandcodes/summaryguidance0208.pdf?view=BinaryStep
2: Check the validity of the document and be satisfied that the prospective, or existing employee, is the person named in the documents presented. Make sure you check the detail such as date of birth. The further document could, for example, be a marriage certificate or a divorce decree.
Step 3: Make a copy of the relevant page or pages of the document, in a format which cannot be subsequently altered.
You can also obtain clarification from The Immigration Enquiry Bureau (IEB) on 0870 606 7766.