Just in case it's helpful anyone else to know, my dad had the DVLA medical with his GP. I think they are tailored to individual medical issues. He has heart disease, so the GP spent a while checking his heart, blood pressure and pulse in his feet (!). For his Alzheimer's, she gave him a mini memory test with the usual questions about the news, asked him to recall a name and address after a short time, and got him to do the clock drawing exercise - which he didn't quite manage perfectly, but the GP said it was good enough as he had done everything else okay and had managed to hold a reasonable conversation with her. So, fingers crossed he will get his license renewed for a bit longer.