Pale juvenile Common Buzzard

Came across this striking pale juvenile Common Buzzard this morning at Pyewipe; the plumage is well illustrated in the Collins Guide and in Dick Forsman's book , in the Handbook of Bird ID Beaman / Madge et al and in Benny Gensboll's Birds of Prey book as well as Lars Jonsson's Birds of Europe but I have only seemed to started seeing these birds in Lincolnshire in the last 7-10 years and they do seem to be occurring more frequently; at this site I saw a pale adult in October 2009 but do not spend a lot of time in the area so have probably missed them in intervening years; this juv was in the same area as two more typical plumaged birds so could they all have been from the same brood?
I have seen pale birds like this one at five different locations in recent years and one bird has been resident since at least 2008 and breeds each year but I have not seen any really pale young in the area -- I would be interested to hear whether these pale birds are appearing in Buzzard populations all around the country or if they are concentrated in the east and if anyone has any theories on why they seem to have suddenly appeared in Britain with such frequency. In the Collins Guide it says of the extreme pale birds found most frequently in the area from North Germany to Southern Sweden.
Always struggling today in 21C heat plenty of shimmer at the range these were taken