Well, Fibula, the way I see it: Youve a clear view from Slieve Donard to the summit of Skiddaw. i would have thought(I dont know the formula) that given the heights of the two mountains, there's nothing to stop you seeing that far. For Scafell/Slieve Donard there's a bit of low lying Isle of Man in the way, but I dont think that should be an insupaerable. The trouble with Black Combe, which is the hill all the books say you can see Ireland from,there is some quite high Isle of Man intervening. I think someone confused a bit of Man with mountains of Mourne, with a bit of wishful thinking, and the claim has been repeated ever since.
   So, couls someone go up Lieve Donard on the next clear day, look to the left of the Point of Aire on Man, and see if you can see Skiddaw?