This is the timber.
According to my rough measurements in gimp it's got an overall twist of about 3° (possible a touch over). This is beyond what I think I can take out with brute force, so I either need to replace the timber (not even sure if I can source another... I need to take a look at this), or plane it true on at least one face.
So... cleaning this up is basically a question of planing a bit, then double checking to see what progress has been made. Rinse and repeat? As of tomorrow even I should have access to an electric planer which may make this plausible.
On the bright side, I don't know how much further it can really twist.
It's one of three beams which support a floor between them (Two spans for the joists). If I can use it as the middle beam, then there's no walls that need to meet it, meaning that I just need to worry about the joist pockets. If I have to use it as an edge, then I need two faces which are true in order to get the outside walls to fit!
