You are missing a big point here, does your dad get DLA mobility component at the higher rate ?(pm if you want).
If he does then he can get a mobility car auto or manual all bills taken care of, if he is not in receipt of it, claim it as after he is 65 he CANNOT claim it even if entitled, it has to be claimed before this age.
The dr's assesment is just that, get it done no problem, refuse and carry on driving and he will be arrested full stop.
Everyone has a legal obligation to tell dvla of anything that does or may affect thier ability as a driver.
I have medical conditions that I have to declare to dvla, which is why my license was limited to 3 yeasr at a time to start with but now till 70th birthday or whatever it is(normal).
Easiest way is to just see the doc get evidence to support you, laugh at your neighbour.
If you do not see the doc then he has a legal obligation to report it to the plod and dvla.
You do not need a assesment, and this is irrelevant as they are not doctors and not medically qualified.
The distinction is they are assesing his ABILITY not his competence, ie is he able to drive safely not is he in need of adaptions.
The doctor will state his opinion and say he is fit/unfit/needs assesment for driving aids.
If he is ok etc then the doc will put that and that will be the end of it.
tabetha