Hi Willogs,
Haven't had any dealings with them but check the small print. A lot of insurers claim that they cover diabetics. What they mean is that they won't turn you down (i.e. they will take your money) but they will not cover any pre-existing medical conditions. That means if you had a claim for flight cancellation or lost luggage, etc, they would pay. But if you claimed for emergency treatment for your diabetes while on holiday, or you had to cancel because of a diabetic emergency, then they wouldn't pay for that because it is a condition you had before you insured with them.