The issue on everyone's mind, of course.
They aren't saying that they'd campaign for a No vote. They have never said that.
This whole referendum business is a distraction. They pointedly failed to put down a Second Reading amendment which did not mention a referendum, but simply rejected the Treaty itself because of what was in it.
In office, they would have signed it without protest and ratified it without a referendum. They are the party of the Treaty of Rome, the Single European Act and the Maastricht Treaty. And they always will be.