Found a role of scrim tape this morning, so that's a good sign.
I spoke to my guy and told him they should have taken the old ceiling down, repacked joists, and done some bonding on the wall. To which he went quiet.
However, I am not willing to go through pulling it all down and doing that. I've got to get the kids back in and move on.
90% of the room is v.good in terms of straight lines. I've told him I'm not paying the £260 for just putting up £50 worth of plasterboard. The room looks great apart from that piece of wall. The finish is lovely throughout.
Not the perfect outcome, but if I had more time....