This situation speaks to the interesting concept - speaking the truth, as you believe it to be true.
I always use the same example -
If you ask someone who believes the earth is flat, if they believe that they earth is flat, they will say that yes, they believe the earth is flat.
Now science, and centuries of experience, proves beyond any doubt whatsoever, that the world is not flat, so the statement is not true.
So is the flat-earther telling a lie?
No, because he believes that what he says is the truth, and therefore he is not telling a lie.
What he says is categorically not true, but because he believes it to be true, he is speaking the truth as he understands it.
It is therefore possible for Mr Johnson to say something that has been proven not to be true, but if he believed at the time that it was true then he is not lying.
This will be the thrust of his defence, and in all reasonableness, it will be very very difficult to prove that he knew what he was saying at the time was untrue, which would make him the liar that so many people accuse him of being.
I believe that at the end of this procedure, the inability to prove that Mr Johnson has knowingly lied to the House, will see him walk away unscathed, and history shows that his skin is more than thick enough to shrug off this situation, and leave his detractors fuming with impotent rage, while he continues to act exactly as he pleases.