EU leaders are set to offer the U.K. a further extension to the Brexit timetable, but the key final date is yet to be decided, according to draft conclusions of the European Council summit to be held on Wednesday evening.

The document, seen by POLITICO, states that the European Council will grant an extension of the Article 50 negotiating period to allow for "ratification of the Withdrawal Agreement." But on the ultimate end date for the extension it says, "Such an extension should last only as long as necessary and, in any event, no longer than [XX.XX.XXXX1 ]." The key date will be decided by leaders when they meet in Brussels Wednesday evening.

The document adds: "If the UK is still a Member of the EU on 23-26 May 2019 and if it has not ratified the Withdrawal Agreement by 22 May 2019, it must hold the elections to the European Parliament in accordance with Union law. If the United Kingdom fails to live up to this obligation, the withdrawal will take place on 1 June 2019."

The draft conclusions reiterate that the extension cannot be used by the U.K. to begin negotiations on its future relationship and that the EU will not contemplate reopening the Withdrawal Agreement — although the EU is prepared to reconsider the text of the Political Declaration. Also, "any unilateral commitment, statement or other act should be compatible with the letter and the spirit of the Withdrawal Agreement and must not hamper its implementation."

One key issue has been whether the U.K. might "go rogue" during an extension and seek to obstruct EU business. The draft states: "The European Council takes note of the commitment by the United Kingdom to act in a constructive and responsible manner throughout this unique period in accordance with the duty of sincere cooperation and expects the United Kingdom to fulfil this Treaty obligation in a manner that reflects its situation as a withdrawing Member State. To this effect, the United Kingdom shall facilitate the achievement of the Union's tasks and refrain from any measure which could jeopardise the attainment of the Union's objectives."

Germany is open to a long extension and will back May's request for more time.

The document states that the U.K. is free to revoke its Article 50 notification "at any time" — an action that would halt the Brexit process.

Prime Minister Theresa May met with her German and French counterparts Wednesday in Berlin and Paris to brief them on the progress of talks between her ministers and the leadership of the opposition Labour Party. After failing three times to win backing for the Withdrawal Agreement from MPs in the U.K. parliament, she last week opted to change tack and open up a dialogue with the opposition to seek a way of resolving the Brexit deadlock.

“Ahead of EU Council tomorrow, the leaders discussed the UK’s request for an extension of Article 50 to June 30th with the option to bring this forward if a deal is ratified earlier," a U.K. government spokesperson said of the meeting with Germany's Angela Merkel.

“The Prime Minister outlined the steps the government is taking to bring the Brexit process to a successful conclusion, and updated Chancellor Merkel on the ongoing discussions with the Opposition."

Germany is open to a long extension and will back May's request for more time, a senior German government official said.

Matthew Karnitschnig and David Herszenhorn contributed reporting.