Hi Ian,
As SarahQ said, except that your insurer is entitled to increase your insurance if they want to. Most insurers won't, but if yours does then I would shop around as there are plenty of others who are happy to insure diabetics with no added premium. However, you do need to advise your insurer as well as DVLA. If you fail to notify your insurer and were to have an accident, your insurer could refuse to pay out on the grounds that you have withheld information about your health.