Mrs May told Parliament she could not take a "no-deal" Brexit off the table as there was no approved alternative yet, and that the EU would be unlikely to postpone Britains exit date — determined by the "Article 50" withdrawal notice — without an exit plan.
Hardline supporters of Brexit in Mrs Mays Conservative party object above all to the fact that Britain cannot unilaterally end the backstop, which would keep it in a customs union with the EU until an alternative way of ensuring an open border is found.
Hilary Benn, an opposition Labour Party lawmaker who is chairman of parliaments Brexit committee, said: "While her door may have been open, her mind has remained closed because she has rejected stopping us leaving the EU with no deal, even though she knows it would be disastrous.
" Jacob Rees-Mogg, chairman of the European Research Group of anti-EU lawmakers in Mrs Mays party, said Britain was most likely to leave without a deal.
Mrs May vowed to be "more flexible" with MPs in trying to agree to changes to the Northern Irish backstop, an insurance policy to ensure there will be no return to border checks between the British province and Ireland.