EMMANUEL DUNAND/AFP/Getty

U.K. Prime Minister Theresa May formally requested a second extension to Britain's Brexit deadline Friday as she continues talks with opposition party lawmakers in London in an attempt to break a months-long deadlock, and a simmering political crisis, in what could be the final act of her two-year term in office.

In a letter to European Council President Donald Tusk, published Friday, May asked for the current extension, which calls for either an exit date of April 12 if her thrice-defeated Withdrawal Agreement isn't passed, or a May 22 departure if it is, to be penciled in for June 30. However, May also said that if she is able to hammer out a deal with opposition Labor Party leader Jeremy Corbyn, and get majority support for any potential deal in Parliament, Britain would reserve the right to leave at an earlier date.

"The government will want to agree a timetable for ratification that allows the United Kingdom to withdraw from the European Union before 23 May 2019 and therefore cancel the European Parliament elections, but will continue to make responsible preparations to hold the elections should this not prove possible," the letter said.

The pound was marked modestly higher against the U.S. dollar at 1.3090 following news of the extension request, as investors bet against a so-called Hard Brexit that would see Britain leave the EU without a bespoke agreement. Gains were capped, however, by early reports from Europe which suggested resistance to the extension request.

May and Corbyn will continue talks for a third day in London today, with both sides expressing the "constructive" nature of the dialog after the Prime Minister reached out to her long-time political rival in order to break the current Brexit impasse.

"Agenda items were customs arrangements, single market alignment including rights and protections, agencies and programmes, internal security, legal underpinning to any agreements and confirmatory vote," Corbyn said in a note to his Labor party colleagues.

The prospect of a confirmatory vote, however, is being resisted by both most Conservative lawmakers and a vocal minority in the Labor party, twenty five of which wrote a public letter to Corbyn urging him to "go the extra mile" in talks in order to reach a palatable compromise as quickly as possible.

"Delaying for many months in the hope of a second referendum, will simply divide the country further and add uncertainty for business," the letter said. "A second referendum would be exploited by the far right, damage the trust of many core Labour voters and reduce our chances of winning a general election."