Autumn Crocus or Meadow Saffron - Long Wood and Velvet Bottom, August 2004
It's not actually a crocus - common names aren't always a good indicator. Colchicum autumnale is a member of the Lily family.
The plants are poisonous but apparently not the usual source* of Colchicine which is used in biochemical research
and is definitely present in the bulbs. Colchicine has been used (and may still be) for the treatment of gout.
Nor is this flower the source of Saffron -
see Crocus sativus for that !)