This afternoon I travelled from Reading to Oxford on the train. Just before we passed through Pangbourne I saw some largish birds soaring over the grassy hills to the north. Though they were too far away to identify properly, they looked like red kites (Milvus milvus).
Red kites have been reintroduced into the Chiltern Hills and are apparently quite common in that area now. Some good pictures of them can be found at Gerry Whitlow's web-site.
Early in 2004, Zoe and I were also on a train to Oxford when we saw three red kites quite close up. They were flying together over a field beside the railway track and their characteristic forked tails were clearly visible to us. One of them even made as if to attack one of the others by flying underneath it, turning upside-down with raised claws, and then dropping away at the last moment.