Strange fruit

I've got a bit of a thing for growing things from pips, inspired by my late father-in-law who grew a beautifully prolific vine from a pip from a Christmas bunch of black grapes.
So far I've only succeeded with a conker and a quince pip, but these fallen fruits under a tree in a suburban street look like a good challenge. The only problem was, I had no idea what they were.
Thanks to one of the knowledgeable people on The Bumblebee Conservation Enthusiasts' Facebook page ( click if you like delectable pictures of bumblebees ! ), I now know they're the fruit of a medlar tree.
So, here's to planting and hoping !