What bird is this?

Thought it was a Plover bird that had been living on our beach, but after zooming in on this photo, I realise it is nothing like one! Nearest I can find in my bird book is a Caspian Tern (winter markings) but they say that they should be 510mm in length, but this bird is a bit smaller than the Black Backed Gulls we have here. More the size of a Plover bird. The description of its beak matches, and it's legs are blackish, from what I can see in one of the other photos. This picture has been cropped fairly hard, so it isn't the sharpest of pictures. But I am going to try for better.