The Government’s approach to Brexit is “chaotic”, the DUP leader said.
Arlene Foster claimed the British Prime Minister had not listened to those who warned that the draft EU withdrawal deal would not work because of inclusion of the Irish border backstop.
The proposed measure means Northern Ireland would continue to follow some EU rules to ensure frictionless north/south trade if no better deal can be found, and has prompted significant unionist opposition.
Remain-backing parties in Northern Ireland including Sinn Féin said the backstop should be banked and a no-deal exit after Monday’s rethink by the British Government would be catastrophic.
Mrs Foster said: “The fundamentally flawed Withdrawal Agreement would have undermined our United Kingdom economy and the Union itself.
“The backstop would have left Northern Ireland trapped as a hostage to the European Union.”
Her party colleague, East Antrim MP Sammy Wilson, added: “Either the legally binding ‘handcuffs’ of the backstop are removed or else this deal will have to be rejected.”
The backstop was designed to ensure north/south commerce and movement between Northern Ireland and the Republic continued unimpeded after Brexit if no better trade deal was agreed.
Pro-Remain Sinn Féin, the nationalist SDLP, Alliance and Green Party said: “We have a shared responsibility to protect jobs, economic stability, the environment and people’s livelihoods.
“At the very least, this means avoiding a hard border, protecting the Good Friday Agreement and hard-won peace of the past 20 years, and staying within the single market and a customs union.
“Therefore, as a basis for this, we maintain that there is a pressing need for the backstop as set out in the Withdrawal Agreement to be banked.
“By contrast, we believe that a no-deal situation would be catastrophic for our economy and society.”
Meanwhile, Sinn Féin president Mary Lou McDonald said: “Theresa May and the British Parliament are deluding themselves if they think that Irish interests will simply be cast aside to facilitate the fantasy Brexit they are pursuing.
“The Irish Government and the EU need to stand by their commitments and defend Irish interests; there can be no hard border, no diminution of our rights and protection for the Good Friday Agreement in all its parts.”
Shouts of “resign” were heard from Opposition MPs as Mrs May concluded her initial statement to the Commons, with a febrile atmosphere sweeping the chamber for the exchanges.
Jeremy Corbyn was urged to do his “duty” and table a no confidence motion in Theresa May.
The Labour leader warned an “extremely serious and unprecedented situation” had emerged after Mrs May pushed back decisions on the Brexit deal, adding: “The Government has lost control of events and is in complete disarray.”
But after he attacked Mrs May for her handling of the Brexit process, Liberal Democrat leader Vince Cable further put the boot in before appealing to the Opposition leader to act.
Mr Cable said: “With the fiasco today, the Government has really lost all authority.
“Let me just say that I and my colleagues will fully support the Leader of the Opposition (Mr Corbyn) if he now proceeds to a no confidence vote, as duty surely calls.”