they are mirrabelle plums aka cherry plums. been a damn good yer for them ive foraged well in excess of 80lb of them !
heres my nipper jack a couple of hous before the ****s! lol
they make a very good jam and are very high in pectin,i used a olive pitter /stoner save the stones and boil them for 5 minutes,then drain the water into your preserving pan,free pectin and its easier than sieving the whole lot,use 1lb of fruit to 1lb of sugar,it sets well .
they also make nice little prunes if dried.a great wine too but the pectin makes it cloudy unless you use pectolase in the fermentation.
as with most plum family they bear in 2 yearly cycles,one year only a few fruits the next tonnes,as long as theres no late frost!