I found a pretty well formed egg on the ground, so of course the question is ‘name that egg’.
It’s largely white and shiny, for scale I included the obligatory 1Euro coin in the photo, but the egg measures about 40mm in ‘height’.

Very interestingly it is splashed with yellow. But a give away is that the yellow is on both the outside and the inside.

So this is not a marking but it shows that the egg has been predated, that’s the egg yolk.
Without the yellow it is a perfectly white egg, around 40mm with a shiny coating. I also found it in my garden so it is from a bird typically found on my watchlist, no guesses for Avocets or Redshanks.
Well the answer, I believe, is that it’s a wood pigeon egg. A very, very common bird indeed.
Who predated it? I would guess either a magpie or a jay. Wood pigeon nests are very open affairs made from a loose gathering of sticks and twigs, normally quite high up in trees, so easily accessible for a predator.

But it’s was nice to find a little clue as to what is going on in the trees around me.