I gave up, and packed up to go to lunch. On my way out, I tugged a loose edge of wallpaper on a different wall and this happened:
"It just came off in my hands Guv!"
A quick visit to YouTube taught me a different method (start steaming at the top!), and most of the rest of the room came off just as easily. I can't believe the difference in progress and difficulty!
So now my sewing space looks like this:
K