Is there a copy of his licence in his records from when he started with the company? To be put on our firm's insurance, we have to show our driving licence.
That won't help if he has since gained any points / been disqualified since then, I suppose, so really the best courses of action are to either phone the DVLA or to ask to see his licence - and (if it is up to you) refuse to let him drive any company vehicles until he does - if he has been banned, but is still driving company vehicles, that could surely have serious implications for your company's insurance, and just imagine the problems if he had an accident and injured, or even killed someone.