Conservative Brexiteers are overwhelmingly backing the deal as it allows Britain, but not Northern Ireland, a more distant Canada-style relationship with the EU.
The small group of Labour MPs considering backing the deal are worried about commitments to matching EU workplace and other rights being watered down, but some today have come out backing the deal.
There is increasing focus on the next no-deal cliff edge – the December 2020 deadline to agree the next bit of the Brexit negotiations.
Many think it will take years to come to a final agreement. And could tomorrow not be the crucial day?
An amendment has been put down delaying approval for the deal until all the necessary legislation is passed, which could take weeks.
We have been following the twists and turns in Westminster on a day when everything felt in the balance.