From conversations I have had in the last couple of hours, I strongly suspect that the bulk of those elected as Tories who voted for a customs union in the indicative votes would not back a customs union amendment to the WAB because they understand that it would wreck the bill. If an amendment does pass, it will do so largely on the backs of those who want a second referendum. They will hope that the addition of a customs union will lead to the deal failing; reviving the prospects of a second referendum.