Rees-Mogg said MPs would then vote either on a motion to back the deal, or on one to approve no deal. He explained:

The debate that follows will be a motion to either approve a deal or to approve a no-deal exit.

That debate on one or other of those motions would run for up to 90 minutes under the existing rules of this House.

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So it with EITHER be a motion to accept the deal OR a motion for no deal.

It will not be a motion to choose between them. This is unsurprising because there is no mechanism in Parliamentary votes to choose between alternatives.