Originally Posted by Owdboggy

Certainly look like plums to me. There are a lot of small wild plums in hedgerows. We have them on ours and they are very edible. Mind we also have some which are as bitter as they come. Only way to tell is to try one when they are properly ripe. they are not poisonous.
There are by the way, Bullace, Sloes and Damsons as well as Plums, all to be found growing wild.