Interesting question.
Why would you think there is a chance of a discount on a car because you have diabetes?
I have never heard about car discounts for any medical condition apart from assistance when you have a disability.
Although diabetes is covered by the disability discrimination act, I do not consider it the type of disability that requires assistance with travel.
No you don't have any entitlement to motability benefits as a result of diabetes. Because diabetes doesn't affect your mobility unless you have a significant diabetic complication like peripheral neuropathy.
Nor do you dave any entitlement to personal independence payments or other disability benefits as a consequence of diabetes, unless you have some other significant diabetic complication like kidney failure, vision loss, amputation. Well managed diabetes should avoid these complications.
Your profile says you are type 2 on insulin. A type 2 diabetic prescribed with medication to treat their diabetes is entitled to a medical exemption certificate to avoid having to pay the prescription charge on any prescribed medication
No you won,t get any kind of discount for a car because of diabetes.
I have bad neuropathy in my feet, I was asked by my gp if I drove because if I did, he would inform the dvla because of this. If I did drive, which I Don, t, I would willing hand my licence back because I would not feel any pressure on the pedals.