Here are just a few of them - from East Berkshire on the left, and from South Hampshire on the right:
So I think I can safely conclude that it is a very good year for cherry plums. Indeed, there appears to be a glut of them, as confirmed by this foodie blog. I don't know what climatic conditions or whatever have led to this.
They are the same size as cherries and look more or less like cherries, but they are plums. They are absolutely delicious and very easy to eat.
I am now on chutney making detail for tomorrow evening.