Whose eggs are these?

We were out walking in the Yorkshire Dales yesterday and sat down on some grass beside a hedge, next to a minor road. We sat for nearly half an hour then, as we stood up to leave, a flash of brown shot out of the base of the hedge and away into  a nearby field. We hadn't time to see what it was as our backs were turned, but we found a nest with 15 eggs in it, tucked into the foot of the hedge. We were wondering what bird occupied the nest and why there are two larger eggs of a different colour. The bird did well to stay there with two people just 4ft away, chatting and feeding.