Surrey,
United Kingdom 
Is this the obedient plant ? Looks similar although foilage looks a bit different than library photos I've sourced any way here some slightly better photos low light so not great and why would anyone grow a field of them?
2 Jun, 2020
Answers
Sainfoin.
2 Jun, 2020
no it isn't Physostegia, it is Onobrychis viciifolia [sainfoin] and is grown as a crop for animal feed/silage but it is rich in nectar and pollen so it is good for bees to produce honey.
It is thought to be a British native or introduced a very long time ago but there has been breeding work done to increase its yield in Victorian times.
2 Jun, 2020
Thank you and sorry about the previous post thinking it was definitely Physostegia.
2 Jun, 2020
do be silly that's the point of asking isn't it. I had totally forgotten about this plant so thanks for raising it again in my memory :o)
2 Jun, 2020
Learn something new every day. Can't figure out why it didn't come up when I Googled "Fabaceae crops", though.
3 Jun, 2020
I've just read my last reply that should have been ''don't be silly'' Oops!
3 Jun, 2020
Drat! And here I thought that I had finally gotten permission! :D
3 Jun, 2020
just for you Tug you have my permission to be silly but stay legal :o))
3 Jun, 2020
Definitely a member of the pea family. I'm thinking some kind of vetch, but I'm having trouble finding matching pictures.
2 Jun, 2020