Egg identification

My daughter found a nest yesterday, on the ground beneath a magnolia tree. She spent a while trying to figure it out, but no luck. I didn't get too close to take the photos, but I would estimate they're about 20–25mm long. We have a lot of blackbirds, robins, bluetits, wrens, finches etc. (Especially at the moment as the garden has been untended for a year while we had some building work done. Seems to have become a bit of a bird paradise, so we're leaving well alone for now!) I didn't think any of them nested on the ground though.

Any ideas?