Summer snowflake,
Leucojum aestivum, seen in the Aston and Remenham areas downstream of Henley-on-Thames during my walk last Thursday. Also known as Loddon lily because it grows close to that river, a tributary of the Thames, it is a native that grows in wet riverside woods and scrub. It is nationally uncommon as a wild plant but because it is commonly cultivated it is often found growing as an escape.
Not the sharpest of photos, but it's not easy when you're kneeling with one knee in wet, black mud!