Mrs May's speech in Belfast yesterday afternoon was a fairly anodyne affair but the Q&A with journalists that followed was the opposite as she ruled out removing the backstop from the Brexit deal.

The Prime Minister said: "I'm not proposing to persuade people to accept a deal that doesn't contain that insurance policy for the future.

"What Parliament has said is that they believe there should be changes made to the backstop."

Mrs May's decision to rule out scrapping the backstop and instead commit to trying to change it - potentially with a time limit or a unilateral exit mechanism - has sparked anger among some Brexiteers in Westminster.

They have responded by saying they will be unable to support the deal if the backstop stays in the Withdrawal Agreement.

Nadine Dorries, a Tory Eurosceptic, summed up their feeling when she said: "A legally binding limit won’t pass in Parliament.

"The Prime Minister would suffer a further crushing defeat. It’s open the Withdrawal Agreement, remove the backstop, or No Deal."

Another told ITV: “It seems the PM pays lip service to help her move to the next stage then goes back on her word.”

MPs voted last week to tell the Prime Minister they would support the deal if the backstop was replaced with "alternative arrangements".

Following Mrs May's comments yesterday there is now plenty of scrutiny of her interpretation of what MPs agreed.

The reaction to her backstop comment represents a potentially major political headache for the Prime Minister and makes the prospect of her Brexit deal being defeated when it is brought back for another vote more likely.

The question in Downing Street now will be purely about numbers: How many MPs will feel as strongly as Ms Dorries and how many could be won over by a change?