Boris Johnson, Jacob Rees-Mogg and Dominic Raab, all of whom had previously rejected May's deal, backed it yesterday.
But 34 Tory MPs still voted against it, as did the Democratic Unionist Party, and despite frantic last-minute lobbying by Tory whips, who offered Labour MPs £100 million ($192m) for their constituencies if they backed the deal, only five Labour MPs voted with the Government.
In light of the defeat, the Daily Telegraph understands that Gavin Barwell, May's chief of staff, has been told by Cabinet ministers it is time to give the Cabinet a vote on no deal or membership of a customs union.
One Cabinet minister said: "Cabinet needs to vote and decide on the Government position. David Cameron did it before the referendum when he asked ministers to put on record their positions. We have got to put our names to something. The Remainers clearly want a customs union as an alternative but there isn't a majority for that; it would destroy the party.
"It's time to be bold, we need to embrace no deal."
As well as tomorrow's conference call, May is expected to hold a Cabinet meeting when ministers will have a second chance to insist she decides on a plan B.
Later, MPs will vote on the most popular alternatives to her deal, following a series of "indicative votes" on Thursday.
Although no one idea achieved a majority, the idea of a customs union lost by just six votes and a second referendum was rejected by 27 votes.
Cabinet ministers are expected to demand a free vote, having been ordered to abstain over the indicative votes this week.
Government sources said May hoped that if a customs union or a second referendum proved popular, hard-core Brexiteers would back her deal to avoid a softer alternative, enabling her to hold a fourth vote on the deal.
What now?
NO DEAL
The EU has given Britain until April 12 to decide whether to ask for another postponement to Brexit. The bloc has called an emergency summit for April 10. Without a delay, Britain will leave the bloc at 11pm on April 12 without a divorce agreement to smooth the way.
DELAY AND SOFTEN
The alternative to "no deal" is to delay Brexit while Britain tries to sort the mess. The bloc is reluctant to have a departing Britain participate in European Parliament elections in late May, but EU Council President Donald Tusk has urged the bloc to give Britain the extension if it plans to seek a softer Brexit that keeps close economic ties between Britain and the bloc — a "customs union pledge".
ELECTION GAMBLE
Britain is not scheduled to hold a national election until 2022, but opposition politicians could try to bring down the Government in a no-confidence vote, triggering a general election, or the Government could pull the trigger if it thinks it has nothing to lose. May promised to quit if her deal was approved and Britain left the EU in May. She will still face huge pressure to resign.
NEW REFERENDUM
Another option considered by lawmakers this week called for any deal to be put to public vote. The idea has significant support from opposition parties and some Conservatives. The Government has ruled out another referendum on Britain's EU membership, but could reconsider if there appeared no other way to pass a deal.
- additional reporting AP
