UK Prime Minister Gordon Brown announced Monday at 7 p.m. he would step down as leader of the Labor party by September.Brown opened his speech by saying the Labor party and Liberal Democrats would enter negotiations to form a "progressive" coalition government.In a remark clearly aimed at the Liberal-Democrats, Brown said electoral reform was urgently needed.RELATED:Analysis: A rather Israeli election crisisLabour, Tories court Lib-DemsEarlier Monday David Cameron and Nick Clegg met face-to-face, as teams of party negotiators tried to hammer out a power-sharing deal. Clegg also met separately with Brown.Clegg commended Brown on his statement, saying it must have been personally very difficult for him to make, and Brown had made it in the national interest. Clegg said he considered the announcement "could be an important element in the smooth transition towards a stable government." He did not commit himself to reaching an agreement with Labor necessarily, however.Some observers suggested that Clegg's party might be open to talks with Labor if Brown agrees to step down, due to Cameron's expected refusal to back sweeping electoral reform.The key issue: Electoral reform, which the Liberal Democrats demand but which the Conservatives fear would banish them to the political wilderness for years to come.It's a critical juncture for Clegg. His position as kingmaker could determine his party's influence not only in the next government but in elections for decades to come, but only if the Liberal Democrats can get their main wish — an overhaul of Britain's electoral system.Proportional representation is critical to Clegg because it would mean his party would gain a greater share of seats in House of Commons. On Thursday, his party earned 23 percent of the vote yet got only 9 percent of the body's 650 seats.Top Conservative Party lawmakers arrived for a meeting in Cameron's office Monday afternoon. Asked if Cameron would be prime minister by Tuesday, lawmaker Des Swayne, an aide to the leader, said: "I hope so."