Going back to the OP, most airlines these days are used to dealing with diabetic pax, and I'm sure Virgin will be no exception. If you keep all your medication, insulin etc packed in a separate bag, preferably a small insulated cool bag, I am sure you will have no problems either at security (keep the doctors letter etc handy) or on board. There may not be fridges on board, but there will be ice, although a cool bag should do the job perfectly well. Make sure you take more medication than you actually need for the duration of the flight, in case of any delays. I have also noticed that many diabetic pax prefer to take their own food, or at least some snacks on board, so they can eat whenever they feel they need to.
Hope this helps.