He should report it to DVLA, I can't see him getting a fine unless he has been in an accident.
The insurance across the country went up last june by over 100% ( major citys only ) rural areas not affected.
If he declares to the insurance that he takes insulin, it should not go up due to the insulin or diabetes.
The way to check is get a quote as normal, then when you have the quote and want to start the policy, say " oh by the way, I take insulin for diabetes, does that make any difference to the price" they will then say no the price is the same.
Hope this helps.
Eliminator