Nicola, I would also say it was either a scavenged dead bird or possibly a sick bird polished off. I've read of Crows killing adult Lapwings, but such behaviour is unusual- I normally see the Lapwings chase off Crows to protect their nests.
One of the reasons corvids are doing so well these days is the abundance of roadkill- drive up any major road + it's littered with dead
Rabbits, Foxes, Pheasants,etc.