Intrigued

I'm intrigued by this giant plant, one of those that has colonised a vacant plot just off the edge of campus. You can see it in its full height in extras, it's about as tall as me. I've yet to identify it, so if anyone can give me any clues...

And in the butterfly department: Small Skipper, Small Tortoiseshell, Ringlet, Meadow Brown, Large White & Small White.

Postscript: Many thanks to all who have suggested what it might be, for a while Mullein was the prime suspect but now @Knottman2 has directed me toward Weld/Dyers Rocket, which I'm confident is what it is. It's more apparent in my extra than in the main image.