Whilst I agree that contacting your dad’s GP may be a good start There is not necessarily an awful lot he will be able to do. The guidance that doctors are given is essentially ‘that we have to tell the patient that they have a legal obligation to report any medical condition that may effect their ability to drive to the DVLA’ if they don’t and continue to drive then we are to ‘try and persuade them to stop’. If this fails we can ‘discuss it with the patients next of kin, with the patients consent’ and if all else fails we can (and only then) report it to the DVLA ourselves – but agin only after telling the patient that is what we are going to do.
This is not without its own problems as it may lead to a breakdown of trust between the patient and their doctor (i.e. the patient may not attend their GP about other serious medical conditions for fear of being dobbed in to the DVLA), so a lot of GPs will be unwilling to do this unless they absolutely have to.
And ultimately the decision whether to revoke or renew a licence lies with the ‘Drivers Medical Group’ at the DVLA, not the patients own GP. Which is the way it should be to ensure a healthy doctor-patient relationship….
Having said all that I don’t think there is anything to stop you dobbing him in anonymously to the DVLA medical bods!