What's wrong with my Cox's Orange Pippin Tree?

[P-M]

Can anyone help me identify what is wrong with my tree. It is approx 5-8yrs old. After a healthy leaf growth and a lot of blossom, the leaves have turned from healthy looking to discolored and sickly looking within a matter of a couple of days. I've attached some photos. The majority of the leaves are affected, but I can see very little in the way of insect infestation. Any help would be appreciated.

[nickdub]

Looks like potassium deficiency to me.

Some stuff in the link below about fertilisers for apples, with a section on this and what to do about it.

http://www.spectrumanalytic.com/supp...pple_trees.pdf