Looks like a vetch of some description, I think it may be Common vetch
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Thanks for the id clarification, AlanS; I found this along a narrow lane with fields on the other sides of the hedges either side, so the agricultural origin would make sense here.
Lat/Lng: 51.77151, -1.46321
OS grid ref: SP371082
Single track lane near High Cogges & South Leigh. Mixture of hedgerow types separating road from fields & new lake/nature reserve.