BRUSSELS (REUTERS) - European Union leaders agreed to grant British Prime Minister Theresa May a new Brexit deadline of Oct 31, diplomats told Reuters after French President Emmanuel Macron opposed summit efforts to give her another year.

Summit chair Donald Tusk tweeted that an extension had been agreed but gave no details as he went to brief Mrs May on the outcome and seek her necessary agreement to the deal.

The late-night deal means Britain will not crash out of the bloc on Friday (April 12) and gives Mrs May more than the three months she had asked for to build a parliamentary majority behind the withdrawal treaty she negotiated with the EU last year.

But Mr Macron's push for a June Brexit and strong opposition to other leaders' preference for a much longer extension that might increase the chances of Britain changing its mind to stay in the bloc meant the meeting ended up with the October compromise.

Oct 31 would correspond to the end of the five-year mandate of the present EU executive commission.

Leaders would meet again in June, EU diplomats said, to assess the situation. Britain could have left by then if Mrs May succeeds in building a coalition for her deal with the Labour opposition - though there is no sign of agreement yet.

In order to continue as an EU member beyond June 1, Mrs May has agreed to organise British elections to the European Parliament on May 23, though it is still unclear if that vote will go ahead and how far it might turn into a virtual second referendum on EU membership that some hope could mean Britain cancelling Brexit.

The other 27 had all but ruled out pitching Britain, and parts of the EU economy, into chaos on Friday. But a drive by Mr Macron to keep London on a tight leash with an extension no longer than to June saw the emergency summit bogged down in late-night wrangling as German Chancellor Angela Merkel and others argued the merits of granting up to a year.

As at a summit last month which put back Brexit for two weeks, several EU diplomats said Mrs May failed to persuade her peers that she could definitely break the paralysis of repeated failures to ratify the treaty within the coming months.

But Mr Macron had told reporters on arrival that he was concerned that letting Britain stay in the bloc longer, notably if it takes part in elections to the European Parliament on May 23-26, posed a serious risk to the functioning of the Union.

"Nothing can be taken for granted," the French President warned.

French officials said the EU faced "blackmail" by hardline pro-Brexit potential successors to Mrs May, such as Mr Boris Johnson.

They might try to sabotage decision-making, and so any longer EU membership must come with tighter commitments from Britain to play fair than were so far drafted into a summit accord.

An aide to Mr Macron warned that France could even be ready to let Britain crash out without a treaty to avoid legal limbo and provide a transition to new trading terms. "Not everything is preferable to a no-deal. A no-deal situation is a real option."

LAUGHTER WITH MERKEL

However, Dr Merkel has urged the bloc to do all it can to avoid such disruption. She said before leaving Berlin that she favoured a delay of "several months" for Mrs May, who has pledged to quit if hardcore Brexit supporters in her own Conservative party drop objections to her "soft Brexit" and help ratify the deal.

Keen to ease tension, Dr Merkel had broken the ice as talks began by showing Mrs May a photo montage on a tablet of both wearing similar jackets when addressing their Parliaments earlier in the day. It provoked mutual laughter as other leaders joined in.

As talks wore on beyond midnight, with Mrs May patiently waiting elsewhere in the building for word on her nation's fate, Mr Macron rallied support for his concerns about a long extension. But most of the other 27 seemed content to offer Britain nine months to a year, several diplomats briefed by participants told Reuters.

"Macron... said anything beyond June 30 would jeopardise the EU and we shouldn't go there," one said, suggesting talks could drag on through the night in the quest for compromise.

Legally, Britain is due to leave on Friday. But leaders said they would not force Britain out in a disorderly departure and that the only question for the summit was how long to postpone.

"If they need a little more time, I think it's reasonable to discuss what that would be," Latvian Prime Minister Krisjanis Karins said, noting that Britain still faced choices - to leave without a deal, accept the deal that its Parliament has rejected three times, or change its mind and stay in the EU.

Mrs May said on arrival that she did not want a long delay: "I want us to be able to leave the European Union in a smooth and orderly way as soon as possible," she told reporters.

Her EU peers, however, are sceptical about her ability to break the deadlock soon and discussed a proposal by Mr Tusk of a "flextension" of nine months to a year. This, some argue, could increase pressure on Mrs May's pro-Brexit critics to back her deal rather than risk Brexit fizzling out.

If Britain does not elect EU lawmakers, it must leave, with or without a deal, on June 1, according to a draft summit agreement seen by Reuters. Otherwise, it would leave as soon as it ratifies the deal, or without one when the extension ends.

France wants a new summit once it is clearer whether or not there will be an early ratification or a British EU vote. An election for 73 British seats in the European Parliament could be a virtual second referendum on EU membership and so offer a guide to whether Britons might end up backing out of Brexit.

BLACK HOLE BREXIT?

EU leaders are exasperated with Mrs May's handling of a tortuous and costly divorce that is a distraction from ensuring the bloc can hold its own against global economic challenges.

Across from the summit venue, the EU executive celebrated its part in funding a global project that produced the first picture of a black hole, prompting no shortage of ironic comments on social media about the juxtaposition.

Blogger Eliot Higgins tweeted: "We're now more certain about what black holes look like than what Brexit looks like."