pea

Can anyone ID this pea it grows in my local park, up from the basement of a large house, which is now unoccupied and turning into a ruin.
First noticed it a few years ago, its probably escaped from the garden that used to be there, and is now overgrown. But I dont know how as it dont seem to set seed.

 

It is a perennial pea, a relative of the annual sweet pea. It is best propagated by digging up some of the roots. Beware though, it spreads by underground roots and can cover a large area in time.

 

Its covering a large area now, any ideas if it a named type. Bit of a job to get down to the basement to dig out the roots, under flag stones.