Pretty sure it isn't but can't think what it is! Jap Knotweed has hollow stems, not usually that shade of green and thicker. Did it flower?

No it isn't. the top photo appears to have flowers and it looks like Pheasant berry [Lycestera Formosa]

A nice plant but can run a bit.

Thank you! No idea about flowering but the pics were taken yesterday at the back of a house I am looking at purchasing. There was some sort of small pinkish flower on it. Would send a picture but cannot see where I can add a pic 😁

That's definitely leycesteria formosa