Given May's inflexibility on the basic contours of the ways in which Brexit is to happen, Labour and other parties said the Plan B may turn out to be a tweaked version of her defeated deal with the European Union, unless she agrees to changes on the basics.
The Scottish National Party (SNP) is trying to rule out "no-deal" and secure a second referendum for which Brexit would need to be delayed.
And what's more, Mr Corbyn has told his MPs not to talk to her ministers either. "She stands by those principles".
Aides later said that the requirement for an independent trade policy was incompatible with membership of a European customs union - something which Labour regards as essential.
On Jan 29, they will debate these plans, and voting on them should indicate whether any of them could get majority support.
If there is a solution to the riddle, it may be for Parliament's backbenchers to find it.
The Telegraph has learned that a delegation of five ministers from the group visited the Prime Minister in No 10 and warned her directly that they were prepared to quit. She says she can't.
"Take no-deal out of the equation and let's get down to doing a solid deal".
A Tory MP said of Corbyn's refusal to talk to May unless she rules out no deal: "He's happy to have talks with terrorists around the world with no preconditions but not to the government during a constitutional crisis".
Labour Leader Jeremy Corbyn delivers his speech during the 134th Durham Miners' Gala on July 14, 2018, in Durham, England. "No longer can it be said that opinion has not moved significantly since the referendum".
But Mr Hammond said it would not be until next week that things became clearer.
Ms Sturgeon responded in a tweet: "So everything is not on the table".
"I remain determined in the name of the European Union to work for an organised withdrawal", Barnier said in Lisbon.
The EU and May's government have agreed to what they call temporary arrangements to avoid a "hard" border, at least until the two sides can reach a final agreement.
And Ms McVey said she asked the cabinet to vote on Mrs May's deal before it was taken to the commons as she could not "put her name on it" and there were "dissenting voices" in the cabinet against it.
Up to now Brexit has not affected the commitment of British investors in Spain but it remains to be seen what happens after the setback at the Parliament and now that the divorce date is getting closer. A fragile and fractured government which is in office but which is certainly not in power.
"To me, the most likely outcome of all of this is an extension of Article 50", Farage told Sky.
The prime minister could also try to deliver a "softer" Brexit that would keep the United Kingdom closer to the European Union - for instance, by staying in the EU customs union.
Corbyn said that, under certain conditions, he would look at options including another referendum - a remark that increased expectations in financial markets that the political chaos would ultimately delay or stop Brexit.