Parliamentary Scrutiny of Leaving the EU

Is not the convention very clearly established that a major treaty change has to be triggered by an affirmative resolution of the House? The fact that that may only be a convention is still something that must be respected. After all, there are lots of conventions, such as the convention that a Government resign if they lose a vote of no confidence. That is no more than a convention, but Members might be a bit surprised if a Government were not to go in those circumstances.