I played it safe and stopped - I waved him on, my hint of sarcasm seemingly lost on him, who smiled and gave me the thumbs up: cheers, mate!
I count myself lucky that he didn't just make the turn and run me over. But how little effort and time it would have taken for him to just get behind me - I'd have cleared the junction in no time, and he'd been on his way just as quickly.
The location? Cheetham Hill, of course. Perhaps I need to try a different route.