"Any intervention by the Labour Party might well have caused the Tories to close ranks against the common enemy"

That is spot-on and is why Labour have yet to bring a motion of no confidence in the government. It would unite the Tories and, given that the DUP have yet to jump ship, the motion would fail and the Tories would be secure. That situation could change if May can't persuade the DUP to accept her deal, which I'm sure they won't in its current form. It would, however, be good to have a better idea of Labour's honest position in all this. We are definitely not hearing enough from Jezza.