A campaign would be of little use as the official line is that any medical is carried out on a case by case basis. I would tend to agree with this as long as there was not a blanket ban on diabetes.
Confirming there isn't a blanket ban seems to be difficult.
You cannot successfully argue for every diabetic to be allowed to get a commercial medical and although I have IDDM I would be the first to object to a campaign to try and achieve this. This may seem strange but not every diabetic is capable of looking after themselves properly and taking away all the restrictions would end up eventually with them being put in place again for everyone.
I sucessfully argued my case for diving and even changed some UK policy after the rules were tightened up to ban diabetics from diving some time ago. By fighting for a case by case medical it was changed so that if you could prove you were fit you could dive.
I have been meaning to start on the MCA but have never got around to it other than preliminary questions, you see, I don't like being told I can't do something by a faceless official who doesn't know me when I know perfectly well I can