The message
from "Peter" contains these words:

Moved into the house 3 years ago and only this year has any fruit appeared
in any quantity on the tree in the garden. However the majority are
shrivalled - any suggestions why? The first year 3 shrivalled grape sized
fruits appeared and none last year. Pictures at
http://peter4007.fotopic.net/c589417.html

It's called pocket plum disease, and I don't think there's any cure.
Our damson got it and went from being a hugely prolific tree to a basket
case:-(

Janet