Turnip sawflies and Bird egg identification query

Yesterday afternoon I was stalking Turnip sawflies, attempting to get a half decent photo but every time the sun went in, and that was often, they disappeared. Got one eventually.



Turnip Sawfly © Gibby Frogett
 

 I had never seen a Turnip sawfly until about 2-3 years ago when there was a bit of plague of them in garden and they have appeared every summer since.


Polygnum © Gibby Frogett

 In bloom in the garden today is the lovely Polygnum, I love the varied shades of colour on this.
Quite easy to grow and the hedgehogs seem to love rooting about this.




© Gibby Frogett

Found this eggshell and you can sort of see the size of it from the walnut shells nearby.
Thought it probably was a Collared Dove or Wood pigeon but not certain.




© Gibby Frogett



Any ideas what this egg is ? © Gibby Frogett

 

Looks like the top of egg is inside, does it look like something hatched or were the contents eaten... what do you think?