Hi Adam and all,
I should have mentioned that the trees we have are mostly Victoria Plum with a few Damson, and these both seem to be the fruit that are suffering quite badly. We started off with around 86 VP trees but we have lost or are losing quite a few, and we had 3 damson trees but these bore very few fruit this year and look as though we won't have them next year, unfortunately. It has been mentioned to me that the trees are just "done", but it would be a shame to lose them.
Many thanks, Andy