Can we see a photo of Russian Thistle (preferably the whole plant in the ground). I have no idea what it is, but it may be called something different in the UK
It’s not actually a thistle, it’s from another plant family. I imagine the one in your neighbors yard isn’t this dry yet.
I’ve seen it on a few safe plant lists on the site. I’d say give it a try; my Russian won’t eat it. (The irony; my Russian won’t eat this Russian plant!)