By Swedd
United Kingdom 
What is this tree/fruit in my garden
9 Jul, 2017
Answers
I'd have said plum too... probably need to ripen more :)
9 Jul, 2017
It's a Cherry Plum. Grows into a massive tree, I have several and they are full of fruit this year. The fruit will darken more and they make wonderful jelly, jam or wine.
See here for details:
https://en.wikipedia.org/wiki/Cherry_plum
10 Jul, 2017
Previous question
« I have maggot looking bugs on top of my begonia leaves. What are they
Do they have grooves in the side, Swedd? They look like a plum of some kind.
9 Jul, 2017