Two points about this thread.
1. This shouldn’t be controversial but, since the era of Elizabeth I, we have had the Civil War and the Glorious Revolution: the choice posited by Robert is not for the PM to take, but for Parliament.
The U.K. constitution is in many ways dysfunctional, but that point is tolerably clear (though that does not stop the executive trying it on: see the dispute over the “meaningful vote”).
2. I suspect the way through this - and an adequately principled one - is the sign up to a CU unless and until both Ireland and the U.K. are satisfied there is a way of solving the Irish border trilemma.
(The Irish border trilemma is that you have to choose one of (a) infrastructure and checks at the NI/Irish border (b) NI in the CU/SM for goods & checks between NI and GB; or (c) U.K. in the CU/SM for goods).
Since eg @iealondon and the ERG are convinced that the Irish border trilemma is soluble (ie you can say “no” to all three) with existing technology, it’s hard to see how they could have a principled objection to that.
And if they don’t trust Ireland, an arbitration mechanism could be devised to decide the matter fairly if there was a dispute. /ends
