Whether any of the alternatives to the deal have a chance of passing depends essentially on two questions - a) will a second referendum be one of the options?, and b) if so, will Labour back it? On a strict reading of Labour's policy as agreed at conference, they shouldn't vote for a referendum at that stage because they wouldn't have yet tried to force a general election, which is supposed to be Step 1. But presumably Corbyn will come under pressure to bend the policy if Labour pro-Europeans feel that they've arrived at the only realistic time at which a "People's Vote" could be secured. He might try to square the circle by giving his MPs a free vote - which would almost certainly lead to the proposal being defeated. Even if he can bring himself to whip his MPs to vote in favour, though, the arithmetic would be tight.
Other than a second referendum, I can't see any of the alternatives to the May deal having a chance of attracting a majority. The Norway Plus idea would certainly be doomed to defeat, because it entails the retention of free movement, which both the Tory and Labour leaderships agree (wrongly, in my view) is inconsistent with the Leave vote in 2016.
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