I can’t get to mine at the moment, it’s packed away at the back of the garage. What I do remember about it is that the knife coulter is attached to one side of the beam with a U-bolt, about three or four inches back from the plough point; the side of the beam that it attaches to has a round profile steel strip rivetted to it so that it will rock sideways when the U-bolt is slackened/tightened.
To explain better, the U-bolt has two nuts which hold a clamping strip against the flat side of the knife. If you slacken one side and tighten the other it should have the effect of moving the knife sideways.
I’m guessing that the rounded strip is missing from yours. Has anyone out there got an Imp plough that they can take a picture of?