The law takes the view that it is the responsibility of each of us to assess our fitness to drive. If we have an accident due to sleepiness, whether this is due to a medical condition, being kept awake by a crying baby or simply staying up late, we are legally responsible, and could face a heavy fine, or go to prison. Nothing in this information absolves a driver from the need to make a personal judgement as to whether or not excessive sleepiness sufficient to impair driving is present, whatever the cause, and if so, not to drive.
If a doctor tells you must not drive as they have concerns about your ability to drive safely, whatever the reason, you must stop driving.
If you continue to drive against GP advice, or in the knowledge that your driving could be impaired by excessive sleepiness, you are probably not insured as you will be breaking the law as defined in Section 88 of the 1988 Road Traffic Act.
© Sleep Apnoea Trust Feb 2018