Theresa May has risked another bitter clash with anti-EU Tories by saying she is “not proposing” to replace the Irish backstop in her Brexit deal.

The prime minister appeared to go back on last week’s Commons vote – to replace the backstop “with alternative arrangements” – by saying she was only seeking “changes”.

Brexiteer Tories have already warned such a compromise would be unacceptable – ruling out either a unilateral withdrawal clause or an end date to the backstop.

Instead, they insist the prime minister must demand that Brussels scrap it altogether and replace it with new – unproven – technology, to avoid the return of checks at the Irish border.

The hardline European Research Group reacted immediately to the speech, in Belfast, saying: “Even if she doesn't mean what she said, we still do.”

Brexit: What is the Irish border backstop?

Until now, Ms May has insisted three options were being considered – a time limit, an exit mechanism, or ill-defined” alternative arrangements” to the backstop.

However, she faced a backlash in Northern Ireland, where most residents and businesses support the guarantee as a way of avoiding a no-deal Brexit.

Asked how she could convince the people of Northern Ireland to accept a Brexit deal which was stripped of the backstop, Mrs May said: "I'm not proposing to persuade people to accept a deal that doesn't contain that insurance policy for the future.

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“What parliament has said is that they believe there should changes made to the backstop.”

The prime minister reiterated her message when she was asked how business leaders could trust her after she “shafted them” over the backstop.

She replied: “You've used the term U-turn in your question: there is no suggestion that we are not going to ensure that, in the future, there is provision for this - it's been called an insurance policy, the backstop.”

Ms May said it would ensure that if a trade deal was “not in place by the end of the implementation period there will be arrangements in place to ensure that we deliver no hard border”.

But one prominent Brexiteer Tory, John Whittingdale, reacted to Ms May’s comments by pointing out she had set up a “working party” to explore ideas that “would not need the backstop”.

“That’s the kind of alternative that it is in the interest, not just of Northern Ireland, but the United Kingdom as a whole,” he said.

The prime minister will set out her ideas in Brussels on Thursday, where she will meet both Jean-Claude Juncker and Donald Tusk, the presidents of the European Commission and Council respectively.

The prime minister also dismissed a threatened legal challenge against her Brexit deal by former Ulster Unionist leader David Trimble, on the grounds the backstop would breach the terms of the 1998 Good Friday Agreement.