Theresa May says she does not have enough support to win a vote on her EU withdrawal deal “as things stand”.
She said she would continue trying to get MPs to back it before putting it to the Commons for a third time this week.
The PM will also order Tory MPs to vote against a bid by a group of MPs, headed by Tory Sir Oliver Letwin, to hold votes on alternatives to her plan.
The government would give MPs time to hold such votes, but Mrs May said she was “sceptical” about the process.
She said the government would not commit to delivering the outcome of the votes but would “engage constructively” with MPs.
“The votes could lead to an outcome that is un-negotiable with the EU,” she told MPs.
“No government could give a blank cheque to commit to an outcome without knowing what it is.”
DUP leader Arlene Foster told the prime minister her party had not changed its position and would not be backing her deal, in a telephone call after this morning’s cabinet meeting.
The prime minister said the “default outcome” remained leaving the EU without a deal.
“The alternative is to pursue a different form of Brexit or a second referendum,” she said.