Yellow Rattle

A yellow rattle, probably Rhinanthus minor, also known as hay rattle, corn rattle or cockscomb. 

This plant is 'hemiparasitic' on some grasses (it will parasitize then if they are available but can grow without them).  Indeed, it is sometimes deliberately added to meadows that are being managed for wildlife because it slows the growth of grass, allowing other plants to flourish.

Photo taken in Reading University grounds, Reading, UK, on 2011-05-13.