Ah Paul this is so frustrating after all the effort you put in to reclaim the wild area.
I would not remove what is there because I suspect the ap has finally or almost finally broken down, in contact with soil organisms.
Your crops are certainly not the worst and greenhouse tomatoes show a mild effect only.
Do a bioassay on a bed with a few broad bean or pea seeds.
Sarah Raven suffered it this year with here fine new bed of dahlia bulbs. She was so upset and has got her MP on it and the NFU, I hope that makes a difference as this stuff is lethal and should not be allowed ever again.
Farmers are supposed not to sell treated material, and they sign an agreement to that effect: your farmer must have done that, unless nobody is enforcing it.
It’s a legal requirement, was a condition for Dow being allowed to sell it again after the original ban.