I thought this was a snowdrop when I saw it but my flower book tells me otherwise. It's a wild plant called spring snowflake. The plants are much bigger than snowdrops and the leaves bright green rather than greyish. It's classed as rare in Britain. Certainly it's the only one I've ever seen! And there's just one primrose on my walk across the fields. It's nestled in a corner down by the stream. It was quite difficult to get near enough for the picture!
Update April 2012: Further research has shown that the plant above is summer snowflake rather than spring snowflake. The three or more flowers in the flowerhead are the indication. Spring snowflake only has one or two. I found one of them in March 2012.