British Prime Minister Theresa May said Tuesday her government was working "extremely hard" to save a Brexit deal that continued slipping out of grasp despite frantic negotiations with the European Union.

May spoke to leaders of London's City financial district with anxiety mounting over the doomsday possibility of Britain crashing out of the 27-nation bloc in March without an agreement.

The British prime minister hopes to seal divorce terms that can maintain frictionless trade -- and assure there is no panic on the markets -- by the end of November.

But the latest in a series of crunch meetings between top negotiators in Brussels on Sunday broke up without a breakthrough a few hours after midnight.

"The negotiations for our departure are now in the endgame," May's office quoted her as telling a reception in the heart of London's financial district.

"And we are working extremely hard, through the night, to make progress on the remaining issues in the withdrawal agreement, which are significant." A UK government source said a deal must happen by Wednesday if there is any hope of an extraordinary EU summit this month to sign the withdrawal agreement.

The crisis could otherwise drag on until a regular EU summit on December 13.

This would dramatically curtail the time May will have to get any agreement past a rebellious British parliament before Brexit day on March 29. The pound dropped to 1.285 dollars from Friday's close of 1.297 on fears of the saga ending in a messy divorce that fails to establish short-term trading rules between one of Europe's biggest economies and the rest of the bloc.

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