Common agrimony (Agrimonia eupatoria) growing in the long grass in Reading University grounds. The flower spikes can grow to over 50cm tall. When the flowers wither they develop into reddish seeds which are covered in little hooks, rather like burdock only smaller:
When I finished taking these photos I discovered four or five of these seeds attached to the hairs on my arm. This plant had several flower spikes and several seed spikes at the same time.
The leaves of the plant look like this:
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-09-05.