Cultivar self-seeding at Wisley gardens
No interactions present.
Lathyrus neurolobus has monojugate (only a single pair of leaflets) leaves. It also has even fewer flowers in the raceme.
This does not look like Marsh Peas I have seen and seems unlikely to be cultivated. There are so many foreign Lathyrus species...
Lat/Lng: 51.31293, -0.47667
OS grid ref: TQ062581