The first gold rule is don’t take on such foreign workers until you have carried out the necessary checks.
Secondly, you must ask for original documents including:
If such documents are not available there are other combinations of documents listed on the Home Office – Immigration and Nationality Directorate website.
Thirdly, the original documents should be checked to confirm authenticity for the employee presenting themselves.
Fourthly, the documents need to be copied. The copy must be permanent if stored on a PC system.
Fifthly, there is a different procedure depending on where the worker is from. Again you should check the Home Office website.