There's a nursery based in Wiltshire that specialises in unusual varieties of native plants.
Natural Selection
http://www.worldmutation.demon.co.uk/plant%20list%2002.htm
what's new for 2003
http://www.worldmutation.demon.co.uk/2003%20additions.htm
unusual British/European plants
Baa
May 21, 2003
I don't know if he still does it but he used to produce a sort of mutation news letter.
Rosemary Castle's Alternatives is a good source of the left of centre wild flowers too
http://website.lineone.net/~altern/