My understanding is this may occur if you have had "
two episodes of severe hypoglycaemia in the last 12 months (where you are completely dependent on other people to treat your hypo)". If this has only occurred once, you may want to talk to the diabetes UK helpline (
https://www.diabetes.org.uk/how_we_help/helpline) because this has only recently changed due to some strong campaigning from them.
The reason for the removal of driving license under these conditions is that you are not deemed safe to drive. Therefore, this would be from the point you are informed not when your license is renewed as this could be up to three years away.
Good luck with getting this overturned.