My neighbor has a damson tree and most of the fruit this year is deformed and flat and when i broke one open there was no stone forming in them and some have a slight yellowing on them, i have looked in my RHS encyclopedia but there is nothing it that matches symptoms. anyone one have any ideas please.
If the flower gets frosted just at the point of pollination it can have some odd effects.
that could be a possible cause
They are miles off being ready - just leave them and they will / should be ok.
It happened a few years ago to a Mirabelle plum in my daughters garden, and the results were not good. Either they dropped off, or the fruits did not swell properly. There was not much to eat.
Apples tend to do better because the blossom opens over a longer period, so hopefully over the course of a week or some of the fruit are ok.
Plums are stupid they sometimes flower a little bit too early and get caught out.