Then, after the same battle on the other side, I could simply undo the top grill retainers; one flat head screw to remove the battery compartment wall, and three trim clips that were thankfully more compliant:
Then came the really tricky bit....with frozen fingers, wiggling the entire bumper to get it off. I found that by pulling the bottom of the bumper, and pulling the top grill forward, a number of satisfying clacks resounded. EDIT: unfortunately the clacks were not good, and I snapped one clip. Maybe don't rock the bumper top-bottom!
But, with another quick view of the video, and with my wife, we managed to pull it off. You have to pull where the body colour rib goes across the front of the bumper (non-startline) and it really comes away in one go.
I paused thinking that the radar sensor may have a wire attached, as I don't have fogs (which do), but the radar sensor is actually on the chassis, not part of the bumper.
I went on to remove my headlights, but I'll post that separately