By Kylie MacLellan and Elizabeth Piper
LONDON (Reuters) - British Prime Minister Theresa May urged MPs on Monday to take a "second look" at her deal to leave the European Union, a last-ditch effort to win over a parliament that looks set to reject the agreement.
The fate of the United Kingdom's March 29 exit from the EU is in the balance before Tuesday when parliament is widely expected to vote against May's deal, opening up outcomes ranging from a disorderly divorce to reversing Brexit.
In the deepest crisis in British politics for at least half a century, May and EU leaders exchanged letters giving assurances on her withdrawal agreement, though there was little sign of a change of heart among rebel MPs.
May used a speech at a china factory in the leave-supporting city of Stoke-on-Trent in central England to say that MPs blocking Brexit altogether was now a more likely outcome than Britain leaving without a deal.
She then returned to parliament, where she asked MPs to give her deal a chance, referring to the assurances she secured from Brussels and warning parliament it risked the break up of the United Kingdom if it voted against the agreement.
"I say to members on all sides of this House (of Commons) - whatever you may have previously concluded - over these next 24 hours, give this deal a second look," she said.
"No it is not perfect. And yes it is a compromise," she said, telling them to think about how any decision will be judged in history books. "I say we should deliver for the British people and get on with building a brighter future for our country by backing this deal tomorrow."
May has refused to budge over her deal despite criticism from all quarters. The agreement, which envisages close economic ties with the EU, has united the opposing sides of the debate - pro-EU MPs who see it as the worst of all worlds and Brexit supporters who say it will make Britain a vassal state.
Turning to her Conservative Party at a private meeting, May again warned MPs against fuelling division in Britain over Brexit and against allowing the main opposition Labour Party and its leader Jeremy Corbyn from winning the upper hand.
"She said ... I just want you to focus on two things: we have to deliver Brexit ... and two that we've got to keep Jeremy Corbyn as far away from Number 10 (Downing Street) as possible," lawmaker Nadhim Zahawi told reporters after the meeting, adding that May was relaxed.
But two Brexit supporters left the meeting early, saying they had not changed their minds on opposing her deal.
LETTER FROM EU
As the world's biggest trading bloc tried to brace for an unpredictable ride, Spain said the EU could agree to extend the deadline for Brexit, but not beyond elections for the European Parliament due in May.
And as part of the effort to get the deal approved by the British parliament, the EU and May set out some assurances in a choreographed exchange of letters on Monday.
The EU told May that it stood by commitments to find ways to avoid triggering the "Irish backstop", an insurance policy to avoid the return of a hard border in Ireland, in their Brexit deal and that this pledge had legal weight.
In a joint reply to questions from May, European Commission President Jean-Claude Juncker and European Council President Donald Tusk said the EU stood by its commitment to try to reach a post-Brexit trade deal by the end of next year in order to avoid using the unpopular backstop.
While stressing that nothing in their letter could be seen as changing or being inconsistent with the draft treaty agreed with May last month, they said a commitment to a speedy trade deal made by EU leaders had "legal value" which committed the Union "in the most solemn manner".
May said the assurances might not go far enough for some MPs and the small Northern Irish party that props up her minority government said it was insufficient.
Nigel Dodds, deputy leader of the Democratic Unionist Party, said he would not back the deal, but his party's aim to get it renegotiated meant it could also not support any move by Labour to call a vote of no confidence in the government.
With a 'no deal' Brexit the default option if May's deal is defeated, some MPs are planning to try to pull control of Brexit from the government.
But though May is weakened, the executive has significant powers, especially during times of crisis, so it was unclear how parliament would be able to take control of Brexit.
If May's deal is defeated and the government is unable to have any amended version passed in the next three weeks, one suggestion is for senior MPs who chair parliamentary committees to come up with an alternative Brexit plan.
"What we need to do is find the solution," said Nick Boles, one of the Conservative MPs behind the plan, who said he would vote for May's deal. "And if the government can't find the solution ... then parliament needs to," he told BBC radio.
(Additional reporting by Jan Strupczewski in Brussels and William James in London; Writing by Guy Faulconbridge and Elizabeth Piper; Editing by Janet Lawrence)