She added that the deal “delivers in ways that many said could simply not be done.” It would put in place a transitional relationship with the European Union through the end of 2020, while a permanent arrangement is negotiated, but the transition period could be extended.
Jeremy Corbyn, the Labour Party leader, called Mrs. May’s agreement “a leap in the dark, an ill-defined deal by a never-defined date.” The continued uncertainty about Britain’s relationship with Europe, lasting at least another two years and possibly much longer, will accelerate the exodus of businesses and investment that is already underway, he said.
“Parliament cannot, and I believe will not,” accept the arrangement, he added.
That view was echoed by Ian Blackford, a lawmaker from the Scottish National Party, who said the prime minister was “trying to sell us a deal that is already dead in the water.”
The lack of support for the deal from lawmakers in both major parties also kept the pound down. “What we need to see is ministers who have not resigned come out and back the deal,” said Jordan Rochester, a foreign exchange strategist at Nomura Securities. “It’s not the P.R. campaign we’ve expected.”
Still, the lack of clarity kept the pound from collapsing, Mr. Rochester said, though calls for a vote of no confidence in Mrs. May did not help. Despite a series of negative headlines through the day, he noted, the pound did not continue to fall.
“There is a buyer out there,” he said. “It’s guys thinking, ‘It’s bad now, but it increases the chance of remain.’ ”