MPs will be asked to vote again on Brexit on Friday but only on part of the deal negotiated with the EU.
They will vote on the withdrawal agreement – covering the “divorce bill”, citizens’ rights and the controversial Irish “backstop”.
But the political declaration covering the UK’s future relationship with the EU will not be put to the vote.
Amid anger from MPs, Andrea Leadsom said it was “crucial” if the UK wanted to secure a Brexit delay until 22 May.
“If we don’t agree the Withdrawal Agreement tomorrow then we will not, so that leaves in doubt the future for the arrangements with the European Council,” she said.
The PM’s deal includes a withdrawal agreement – setting out how much money the UK must pay to the EU as a settlement, details of the transition period, and the backstop arrangements – and a political declaration on the way the future EU-UK relationship will work.
The vote would not allow Parliament to ratify the withdrawal package, because Brexit legislation allows this only after the passage of a “meaningful vote” on both the Withdrawal Agreement and a Political Declaration on the future relationship.
And some MPs questioned its legality, with Labour’s Valerie Vaz saying “on the face of it breaks the law”.
“This is no way to run a government,” she told MPs.
Commons Speaker John Bercow said it was a “new” motion and complied with his ruling that he would not allow a third “meaningful vote” on “substantially the same” motion as MPs had already rejected by historic margins twice.
Commons Leader Mrs Leadsom told MPs that the European Council would only agree to extend Article 50 – delaying Brexit – until 22 May if MPs approved the withdrawal agreement by 2300 GMT on Friday.
“It’s crucial therefore that we make every effort to give effect to the Council’s decision and tomorrow’s motion gives Parliament the opportunity to secure that extension,” she said.
“I think we can all agree that we don’t want to be in the situation of asking for another extension and facing the potential requirement of participating in European Parliament elections.”
But she faced anger from MPs. Labour’s Mary Creagh described it as an “extraordinary and unprecedented reverse ferret of the commitments that have been made..that we should have our say on both items together”.
Her fellow Labour MP Stephen Doughty described it as “trickery of the highest order”.