When I removed the plasterboard, I also removed the fake beam. The plumber is lined up to move the pipe so it runs along the wall, rather than slap bang through the middle of the room. But the real beam was still there. It had gone underneath the plasterboard, so also underneath the wallpaper. But that was a bit of an issue, as that meant you couldn't easily remove either plasterboard or wallpaper from between the new beam and the old beams.
I wandered if I should just try to cut off the plasterboard and wallpaper straight, and plonk a little decorative wood moulding over it. But it's not easy to do that. You can't really get to it very well! And when I went and had a try, I ended up taking out the entire plasterboard. And I think I'll proceed that way. I may well just add wood moulding afterwards anyway! It looks a bit odd; a varnished beam, then some 1.5 cm, and then a Victorian beam. But we'll see! It's still a bit of a work to remove all of it! And I will have to try to saw off the nails. I won't have to be bored anytime soon!
On the left the gap is cleared; on the right, plasterboard and wallpaper remains