My doctor said no one can do anything without my Dad's consent (which he won't give)
That may be so if there's no diagnosis because your dad refuses to go to the doctor. You can't
make him go to the doctor, and you can't
force him to get a diagnosis.
But if there is a diagnosis of a notifiable condition, "no one can do anything" goes out the window, though plenty of doctors don't want to do anything anyway (see previous posts).
Older discussions turn up many and varied outcomes:
"My husband's GP contacted the DVLA even before diagnosis when he noticed that my husband was suffering confusion. The DVLA immediately wrote telling him to return his licence."
https://forum.alzheimers.org.uk/showthread.php?57597&p=756705&viewfull=1#post756705
"I contacted the GP and he declined to advise. I contacted the DVLA and all they did was write to Dad asking if there was a problem and did he feel he should stop driving. Of course the letter went in the bin."
https://forum.alzheimers.org.uk/showthread.php?3214&p=30508&viewfull=1#post30508
Here's a case with no diagnosis, yet contacting DVLA led (somehow) to a cancelled licence, and an agry parent:
"During this time mum was still driving and I contacted the DVLA because I was worried about her and her licence has been cancelled. Mum worked out that I had contacted the DVLA (I don't know how) although I consistently denied it and she grew very stroppy with me. She even contacted my brother (who lives 50 miles away) and got him on her side. At Christmas she embarrassed me dreadfully in front of my grown up children by accusing me of telling the DVLA about her."
http://forum.alzheimers.org.uk/showthread.php?91596
"I had contacted the DVLA, hoping to get a message from someone 'in authority' (i.e. NOT her children!) to say that she should stop driving, or at least take an assessment, which she would never have done. 6 weeks after waiting for a reply, the DVLA wrote to say they were writing to her GP, and the reply could take ANOTHER 6 weeks..."
https://forum.alzheimers.org.uk/showthread.php?86018&viewfull=1#post1168185
If you do contact the DVLA again, maybe better to do it using the online form specifically for that purpose, rather than by phone. Although if they have recently sent him a form anyway, maybe they won't see the point of sending him another, so who knows.