May briefed her European counterparts on the exit road for Britain and left leaders with many uncertainties about the divorce because Britain has yet to trigger the two-year negotiations for "Brexit" — and confirmed she is unlikely to do so until the end of March.
"It's in the interests of the U.K. and the EU that we continue to work closely together," said May, who immediately faced opposition.
French President Francois Hollande insisted that the EU would not surrender the bloc's core values just to keep Britain close as a future ally.
"I have said so very firmly: Mrs. Theresa May wants a hard Brexit? The negotiations will be hard," Holland said.
German Chancellor Angela Merkel also chimed in saying that "In practice, that will be a tough road."
Britain's June 23 breakup referendum has forced the 27 other nations to plot their future without a major but often recalcitrant member state. European leaders have grumbled that Britain's tardiness in starting the negotiations slow down their own planning for the next few years.
Merkel said the other leaders would underscore the urgency and would "make clear again: We are waiting for the notification from Britain."
The 27 leaders already had their first summit without Britain in Bratislava last month. May told the leaders Thursday they had to realize that even if they all agreed on issues they should not expect Britain to automatically jump on board at official summits of 28.
Once May activates the exit clause — Article 50 in the EU's governing Lisbon Treaty — negotiations on the terms of Britain's departure would run for two years. The time frame could be extended, but only if the 27 remaining member states agree unanimously.
The Brexit referendum to leave the EU was a milestone in the history of the bloc and the disentanglement is expected to be long, difficult and confrontational.
Still, EU President Donald Tusk, who chairs the summit, reiterated that Britain could still reconsider when asked if May could still turn back the clock. "If it is reversible or not, it is in the British hands. I will be the happiest one if it is reversible."
He said that he hoped "she will also realize that the European Union is simply the best company in the world."
May said Britain would continue to be a responsible member right up to the day it leaves the EU. "I'm here with a very clear message. The U.K. is leaving the EU but we will continue to play a full role until we leave."
Like Hollande, Tusk vowed last week not to compromise on the bloc's principles in negotiating Britain's departure and warned that London is heading for a hard exit.
He insisted that Britain can't hope to both stay in Europe's single market of seamless business and restrict the movement of EU migrants, saying there would be no compromises.
May has appeared to signal that her government would prioritize controls on immigration over access to the European single market, an approach informally called a "hard Brexit."
EU Parliament President Martin Schulz said Thursday that the bloc's fundamental freedoms "are inseparable."
"I refuse to imagine a Europe where lorries and hedge funds are free to cross borders, but citizens are not," Schulz said.
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