Hope this pic is genuine ...
Albino fallow are very rare. Pure whites are not so. From my understanding albino is a total lack of pigment which can bring health problems. Whites have white pigment.
It is probably a park fallow bred for white colouring. Lovely specimen with excellent antlers.
For a pretty concise book on fallow see:
Fallow Deer
Donald and Norma Chapman
Some years ago here in Kansas, an albino deer was seen and videotaped. The Kansas Fish & Game Department, requested that no one shoot it in the upcoming deer season, but it disappeared and was never seen again after deer season.
I saw a wild red deer albino stag near Braemar some years ago. Scraggy looking beast but impressive nevertheless. There are quite a few legends about them in Scottish folklore and they are said to possess magical powers.