Brexit Summit Opens Day After Legislative Setback for May -- 2nd Update

European leaders at a two-day summit in Brussels are set to approve a hard-won divorce deal with the U.K. that opens the door to trade talks.

But as British Prime Minister Theresa May took what was expected to be a victory lap over the agreement Thursday, she was forced to grapple with a legislative defeat the night before in London that threw up a new hurdle.

Members of her Conservative Party joined opposition lawmakers and voted to guarantee Parliament the power to vote on whether to accept any final Brexit deal, a political embarrassment that underscores the extent to which she is being squeezed by factions in her party and in Northern Ireland, all of which want very different versions of Brexit.

Arriving at the summit, Mrs. May said she was disappointed the government lost the vote on an amendment to the EU withdrawal bill, its flagship Brexit legislation, but noted the bill was still making good progress.

"We are on course to deliver Brexit. We are on course to deliver on the vote of the British people," Mrs. May said, referring to the June 2016 referendum in which Britons chose to leave the bloc. Over dinner with EU leaders, Mrs. May said that while many viewed the last few months as a sign of how difficult the future negotiations would be, she believes that the progress the U.K. and the EU have made shows what can be achieved with commitment and perseverance on both sides. Her comments were greeted with applause from the other EU leaders, officials said.

After Thursday night's dinner, Mrs. May said there had been "very good discussions" and she was now looking forward to quickly starting negotiations on "our future trade relationship and security relationship."

German Chancellor Angela Merkel said the bloc's leaders "made clear that Theresa May made good offers" that can allow the negotiations to move ahead.

"But there are still many outstanding issues. We'll talk about it tomorrow," she added.

The push by Parliament to weigh in on the final deal complicates already difficult matters even further as the U.K. and EU prepare to plunge into tricky trade talks. It opens the path of negotiations to influence by lawmakers with competing visions and raises concerns that London won't be speaking with one voice.

"As soon as she negotiates something, she has to go to the Parliament to get approval. This just makes it more complicated for the U.K. government," said Luxembourg Prime Minister Xavier Bettel. He said the EU won't renegotiate the Brexit deal if the British Parliament rejects it.

An EU official said it wasn't in Brussels' interest to negotiate with a weak leader. "I don't think it's good that the prime minister who is negotiating with us is losing votes in the Parliament," the official said. "It's never good. We need a strong negotiator on the other side."

The divorce deal reached last week after six months of tortuous talks leaves many issues largely unresolved, including how to avoid a hard border between EU-member Ireland and Northern Ireland, which is part of the U.K.

Mrs. May and her cabinet will meet next week to discuss for the first time their approach to the next phase. But the more clearly Mrs. May lays out Britain's position, the more she risks dividing a cabinet already fractured over whether they want to pursue a future relationship with the EU that is closely aligned or more distant.

A senior French official said that while there was some sympathy for the troubled political waters Mrs. May has to navigate at home, the EU will not change its negotiating position.

Nicky Morgan, one of the pro-EU Conservative lawmakers who backed Wednesday's amendment, said the development makes it more likely the U.K. will end up with a closer relationship with Brussels than it would have otherwise.

"This has made it very clear that there are a group of people in the Conservative Party who are prepared to break ranks and rebel over something they feel really passionate about," Ms. Morgan said. The majority of lawmakers won't support an extreme Brexit, and without a majority in Parliament, Mrs. May must take that into account as she negotiates with the EU, she said.

The defeat could also embolden more pro-EU Conservative lawmakers to vote against the government, creating further headaches for Mrs. May ahead as she tries to push more of the Brexit legislation through Parliament. Next week, lawmakers will vote on another controversial amendment to the legislation, a relatively minor detail of exactly what time and date the U.K. should leave the bloc in 2019.

Jacob Rees-Mogg, a euroskeptic Conservative lawmaker, said the development was a political embarrassment for Mrs. May, but that in the long-term, it wouldn't have any serious implications for Brexit.

"She's always had to do a balancing act between pro-EU Tories and euroskeptic -- it doesn't change the weighting of that," he said, adding there are many more euroskeptics than pro-EU Conservatives.

If anything, he said, a final vote on the deal increases the likelihood of a Brexit with no ties to the EU, because if Parliament votes down a deal, the U.K. will leave without one. "They want to be careful what they wish for, the pro-EU lot," he said.

Dutch Prime Minister Mark Rutte said he was confident Mrs. May will still be able to deliver on what she promises in Brussels, because there is a "widespread support" in the U.K. for a "reasonable negotiated exit of Britain from the EU."

He said the deal she sealed last week in Brussels proves she is a "formidable politician" who shouldn't be underestimated.

--Emre Peker and Laurence Norman contributed to this article.

Write to Jenny Gross at jenny.gross@wsj.com and Valentina Pop at valentina.pop@wsj.com

(END) Dow Jones Newswires

December 14, 2017 20:07 ET (01:07 GMT)