PRIME Minister Theresa May is to travel to Europe to seek concessions on her Brexit deal, after calling off a crunch House of Commons vote in which she was expected to go down to a heavy defeat.

In a statement to MPs, Mrs May also said the Government was stepping up preparations for a possible no-deal Brexit.

And she said that MPs who were threatening to vote against the deal she secured with Brussels must ask themselves the fundamental question: "Does this House want to deliver Brexit?"

If the answer was yes, she said that they needed to consider whether they were prepared to make "compromises" in order to make good on the 2016 referendum vote to leave the EU.

Mrs May's statement came amid dramatic scenes at Westminster, as news of her plan to postpone Tuesday's "meaningful vote" broke just minutes after Downing Street had insisted it was going ahead.

It is understood that the PM had been warned that she faced a large-scale defeat when MPs voted at the end of five days of debate in the Commons on her plans.

She spoke with her Cabinet colleagues by a telephone conference call before addressing the Commons.

Speaking to MPs, Mrs May accepted that there was "widespread and deep concern" over the backstop arrangement, designed to keep the Irish border open if the EU and UK fail to strike a wider trade deal.

If the vote had gone ahead as planned, the Government would have been defeated by a "significant margin", she said.

"We will therefore defer the vote scheduled for tomorrow and not proceed to divide the House at this time."

Mrs May said she believed there was "a majority to be won" in the Commons on her deal, if she is able to "secure additional reassurance" on the backstop, and that this would be her focus over the coming days.

But she insisted: "There is no deal available that does not include the backstop."

Mrs May said she had spoken by phone with European leaders over the weekend and will meet others, as well as the chiefs of the European Council and Commission, before the EU summit opens in Brussels on Thursday.

"I will discuss with them the clear concerns that this House has expressed," she said.

The Government was also looking at "new ways of empowering the House of Commons" to ensure that any provision for a backstop has "democratic legitimacy and to enable the House to place its own obligations on the Government to ensure that the backstop cannot be in place indefinitely", said Mrs May.

She added: "If you take a step back, it is clear that this House faces a much more fundamental question.

"Does this House want to deliver Brexit? And if it does, does it want to do so through reaching an agreement with the EU?

"If the answer is yes, and I believe that is the answer of the majority of this House, then we all have to ask ourselves whether we are prepared to make a compromise.

"Because there will be no enduring and successful Brexit without some compromise on both sides of the debate."

A spokeswoman for European Commission president Jean-Claude Juncker poured cold water on hopes of a renegotiation of the Withdrawal Agreement, reached after more than 18 months of talks.

In a press briefing in Brussels, Mina Andreeva said: "As President Juncker said, this deal is the best and only deal possible.

"We will not renegotiate - our position has therefore not changed and as far as we are concerned the United Kingdom is leaving the European Union on March 29 2019."