The thread is a little old now but by sheer chance I was looking at a Native Plants website and spotted a reference to BLACK MUSTARD ( BRASSICA NIGRA) which is stated as being native to my area (NW Hants).
I also spotted on a seed website the same beast, listed as "Hot, spicy seeds used in Indian dishes or crushed to make mustard" the website is
http://www.nothing-but-seeds.co.uk/Herbs.htm
