European Union leaders will grant Prime Minister Theresa May a second delay to Brexit but they could demand she accepts a much longer extension as France pushed for conditions to limit Britain's ability to undermine the bloc.
May dashed to Berlin and Paris to ask Angela Merkel and Emmanuel Macron to allow the world's fifth-largest economy to put off its divorce from April 12.
It was not immediately clear what Merkel and Macron, Europe's two most powerful leaders, agreed with May but an advance draft of conclusions for Wednesday's emergency EU summit said Britain would be granted another delay on certain conditions.
May has asked the EU for a Brexit delay to June 30 but the draft left the end-date blank pending a decision by the other 27 national leaders on Wednesday in Brussels.
"People are tired and fed up (with Britain's indecision) - but what to do?" one EU diplomat said. "We won't be the ones pushing the UK off the cliff edge."
Another EU official involved with Brexit said no European power wanted the chaos that they fear a "no-deal" exit would sow through financial markets and the EU 27's $US16 trillion ($A22 trillion) economy.
"Nobody wants to pull the plug by 13th April," said the official. "But for how long - I don't know. And France will ask a lot of questions in Brussels."
Irish Prime Minister Leo Varadkar said Macron would not veto May's extension but wanted conditions attached.
Earlier in the day, May met Merkel at her riverside Chancellery, a short walk from Berlin's Brandenburg Gate, and departed with a warm exchange of kisses.
While they discussed Brexit, Germany's opposition liberal FDP party drove an advertising van past the Chancellery with a slogan reading: "Dear Theresa May. Just do it. Stop Brexit. Make the most of Europe's opportunities."
In London, British Solicitor General Robert Buckland said May would "listen carefully" to any constructive suggestions made by the EU on the length of the extension.
He conceded the government might not have managed to ratify an exit deal in parliament before European elections are held on May 23-26.
According to the draft conclusions, if Britain didn't take part in EU parliamentary elections properly, it would have to leave on June 1, 2019.
Unable to convince enough of her own Conservatives of the merits of her deal to get it passed, May is courting Jeremy Corbyn, whose Labour Party wants to keep Britain more closely tied to the bloc after Brexit.
Labour's demands include keeping Britain in a customs union with the EU, something that is hard to reconcile with May's desire for Britain to have an independent trade policy, and potentially a second referendum on any deal.
After Tuesday's round of talks, Labour said it had not yet seen a clear shift in May's stance.
Meanwhile, British MPs on Tuesday approved by a 420-110 margin May's plan to seek to delay Brexit to June 30 while she tries to strike a compromise with Labour.
The government was forced to hold the vote after parliament passed a law on Monday giving themselves power to scrutinise and make changes to May's request to extend the Article 50 negotiating period a second time.
