it is a wild [native] Vetch, from the foliage I'd go for tufted vetch Vicia cracca. it is a member of the pea family . it will have grown in the fields where the sweet peas were growing. they produce pods from each flower.

Sbg, many thanks for your reply. We also thought it looked like vetch. I have just emailed her to let her know what you said!
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