That means Mrs May would have needed Labour votes to succeed. However, the Labour leadership has been adamant that it opposes the deal and wants a general election. Convincing up to 100 opposition members to rebel and vote with the Government would have been a very tall order.
While defeat seemed certain, the hope had been that it would have been small enough for the Prime Minister to survive and head to Brussels to renegotiate.
However, Downing Street has grown worried that the defeat would be too heavy for Mrs May to carry on after. Since the original vote was delayed, Mrs May has been trying to win concessions from the EU before her deal was put to Commons.
However the key issue, the Irish backstop, is not open for renegotiation. The demands from the Brexiteers for a time limit or a unilateral exit mechanism would render the backstop incapable of performing its intended job and so the EU will not allow it.
Nor is Brussels willing to reopen the legally-binding Withdrawal Agreement more generally. It fears demands from member states over issues such as fishing and Gibraltar.
The European Council and Commission chiefs wrote a letter to Mrs May, which was published yesterday, saying they were “not in a position to agree to anything that changes or is inconsistent with” the Withdrawal Agreement, but they set out in a series of “clarifications” how the backstop would be temporary and was “suboptimal”.