Hi
@Bettusboo GP's cannot suspend licences - they can advise against driving or if they think your dad is a danger to himself or others they can contact DVLA and advise the removal of his licence. Cases of safety like this are the exception to their duty of confidentiality. It may be worth contacting the GP and finding if they have contacted DVLA and in what capacity.
When DVLA was notified re my MIL's dementia they sent a form for her to complete. It gave a time limit to reply and stated that if she did not reply her licence would be removed. If this is the kind of letter your dad had it is likely he no longer has a valid license.
If his license is no longer valid, then, whether the insurance company have been notified or not, the insurance is invalid and they will not pay out if there is an accident.
If he is still driving without a licence and if this is something he would never normally have done then he would appear to have lost capacity to make that decision. I have known several people use a variety of options to stop their PWD driving. One friend locked away the keys, another parked the car on a different street and for her loved one it was out of sight out of mind, another put an imobiliser boot on it and blamed the council. Be creative, you know your dad best, that will help you find a solution that works for you both. Good luck.