Theresa May's Brexit deal was defeated for a second time in the House of Commons on Tuesday night | Leon Neal via Getty Images Theresa May requests Brexit extension until June 30 Prime minister says she wants MPs to ratify deal next week.

Theresa May still hasn't given up on her Brexit deal, but warned she is “not prepared” to delay Brexit any longer than three months.

May requested an extension — until June 30 — of the deadline by which the U.K. must reach a deal on its departure or be expelled automatically from the bloc with no safety net. EU27 leaders were expecting the request, but it is far from clear how they will respond. They are due to discuss the extension issue on Thursday at a European Council summit in Brussels.

May's request, made in a letter to European Council President Donald Tusk, describes a still-complicated and highly uncertain legislative process that she hopes to undertake in order to win ratification of the Brexit deal, which the U.K. parliament has twice rejected by massive majorities.

In her letter, May acknowledges that an unexpected ruling by the speaker of the House of Commons, John Bercow, has made it impossible for her to bring the deal back to parliament for a third ratification vote this week, thereby requiring her to request the extension.

May suggests that formal approval by the European Council of additional assurances regarding the backstop provision on the Northern Ireland border would constitute sufficient changes to the deal for her to request another vote. She also writes that she would put forward a new motion to parliament along with additional assurances by her government.

"If the motion is passed, I am confident that Parliament will proceed to ratify the deal constructively," she writes.

The EU27 are unlikely to share her confidence.

Not only has parliament rejected the treaty twice before, but the second defeat took place after British MPs were fully aware of the new assurances that May had agreed with Brussels. There is little new to persuade them, though May's hopes seem to hinge on finally clinching some deal with the Northern Irish Democratic Unionist Party, whose MPs prop up her government.

And her letter is filled with conjecture and uncertainty about the immediate next steps in the legislative process — a stark contrast to the certainty and predictability that EU27 leaders have set as a precondition for granting an extension. May also says nothing about what might happen if she fails, once again, to win ratification.

A note circulated in the College of Commissioners urges that the 27 leaders offer the U.K. a simple, binary choice.

"Any extension offered to the United Kingdom should either last until 23 May 2019 or should be significantly longer and require European elections," the note, obtained by POLITICO, says. The May date is significant because it marks the start of the European Parliament election.

The document argues that "this is the only way of protecting the functioning of the EU institutions and their ability to take decisions," referring to concerns that the U.K. could jeopardize the legitimacy of the next European Parliament, potentially paralyzing EU lawmaking, if it is still a member of the bloc on election day but doesn't take part in the ballot.

In their deliberations, EU leaders must also take account of the U.K.'s legal right, confirmed by a decision of the European Court of Justice, to unilaterally withdraw its notification of its intention to leave the EU. Such a move, regardless of any extension agreement, could cause havoc for the institutions.

In her letter to Tusk, May acknowledges the EU's previously expressed position that a longer extension — beyond the seating of the new European Parliament in early July — would require the U.K. to participate in the European election. In the House of Commons on Wednesday, May argued strongly against that.

“I do not believe such elections would be in anyone’s interest,” she told MPs. “The idea that three years after voting to leave the EU, the people of this country should be asked to elect a new set of MEPs is, I believe, unacceptable. It would be a failure to deliver on the referendum decision that this house said it would honor.”

Her intervention was taken as an implicit signal that she would resign if MPs reject her withdrawal deal when it returns to the House of Commons a third time next week.

“If that vote is passed, the extension will give the house time to consider the withdrawal agreement bill. If not, the house will have to decide how to proceed. But as prime minister, I am not prepared to delay Brexit any further than 30 June.”

EU27 leaders have never formally discussed the extension issue, but officials have been preparing for a robust debate on the merits, risks and potentially unforeseen consequences of either a short or longer delay. While the EU27 can only grant an extension by unanimity, the EU treaties are silent on all other aspects of the decision. They could potentially make a counter-offer to the U.K., or offer May a take-it-or-leave-it alternative.

While the leaders' discussion is scheduled for Thursday afternoon during the summit, they are unlikely to make a decision until closer to the deadline. Several have expressed the view that the U.K. must provide a clear and convincing reason for an extension, and some have said that a short extension should be granted only if the House of Commons has already ratified the Withdrawal Agreement and Political Declaration that make up the Brexit deal.

European Commission President Jean-Claude Juncker told German radio on Wednesday morning that EU27 leaders will likely not make a decision on extending the Brexit negotiating period at this week's summit and woule potentially hold another meeting next week, just before the March 29 deadline, to decide.

“My assessment … is that the European Council this week won’t come to a decision and we’ll probably have to meet again next week because Mrs. May doesn’t have approval for anything — not in her Cabinet and not in parliament,” Juncker said. “As long as we don’t know what Britain could say yes to, we can’t come to any decision.”

Council officials said they could organize a special summit within 24 hours, leaving open the possibility of a dramatic event on the day of the U.K.'s prescribed departure.

Tom McTague contributed reporting.