Relatively large. Beigy colour with brown speckles. Found near wetland and ponds.
No interactions present.
A 1985 Hamlyn Concise Guide, and this looks a reasonable match in size and pattern to a Black-Headed Gull, so that would be my guess. However both Coot and Moorhen (amongst others!) look similar, though it's perhaps a bit large (I estimate a little over 50mm on the long axis) for the latter.
The 2p piece used for scaling is around 25mm across, so the egg must be around twice that on the long axis. Crossbill eggs are said to be around 22 x 16 mm (BTO site) - much smaller, surely?
I would agree - also this is a very well recorded WWT site and to everyone's knowledge, no crossbills recorded here!
Lat/Lng: 51.6642, -4.1268
OS grid ref: SS530982