Vetch with tine white flowers
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A picture of the pods would make the agreement easy.
My Flickr photos...
Specifically, the pods of Vicia hirsuta are 2-seeded, and those of Vicia tetrasperma are, as you might expect, 4-seeded.
However hairy tare can also be distinguished from slender and smooth tares by the greater number of flowers in an inflorescence, the smaller flowers, and the paler flowers (but they can still sometimes have a distinctly bluish cast). These aren't as neatly binary as the number of seeds, but your plant does match hairy tare.
Unfortunately I didn't see any pods and I came across this while taking a short break on a long drive home. Next time I will look for some.
I took the images using a magnifying macro mode as the flowers were too small for my camera to focus on. They were in the area of 2-3mm.
Lat/Lng: 53.5615, -0.8475
OS grid ref: SE764078
Growing in profusion along river bank