Driving while in early stage of Alzheimer's

My father a young man of only 58 is showing signs of Alzhimer's disease but we are as yet in limbo regarding proper diagnosis of it.  He's recently gone for a head scan and shall have the results in 10 days.  My question for anyone out there is that he is at present driving about the place, frankly can't keep him at home at all.  Always needs to be off out and spinning around.  He can't sit still.  It has come to my attention that he looses concentration whilst driving as in looking around the place, or reading particularly text on passing vehicles or buildings.  He is really in all honesty a danger on the roads for himself and others.  He has put some marks on his car and can't explain how they got there!  My brother travelled with him recently and saw first hand our father's lack of judgement while he scraped his car off a wall..... so million dollar question how do I take the car off him and prevent him from driving?I welcome any advice and many thanks for replying to my post.