Liberal Democrat leader Nick Clegg said it would be “preposterous” for Gordon Brown to stay on as prime minister should his Labour Party come in third in the popular vote in Britain’s election next May 6.

After the British party leaders debated on television for the first time two weeks ago, Clegg emerged as a serious contender to both major parties. The Liberal Democrats are now set to win more votes than they ever have yet Britain’s archaic electoral system will probably deny them much seats in Parliament. In spite of Labour’s waning popularity, it might well come out as the biggest party once again.

“There are now indications Labour might come third in terms of people voting for the different parties,” Clegg told the BBC yesterday. “It is just preposterous, the idea that if a party comes third in terms of the number of votes it still somehow has the right to carry on squatting in No. 10,” the premier’s Downing Street office, “and continue to lay claim to having the prime minister.”

The election is increasingly likely to produce a hung parliament, one in which neither party manages to gain an overall majority. Both Labour and the Conservatives will probably try to come to a coalition with the Liberal Democrats under such circumstances. Although Clegg is said to sympathize with the Tories personally, his party leans more to the left and prefers to work with Labour.

Prime Minister Brown has touted the Liberal Democrats with promises of electoral reform in recent weeks, apparently anticipating the need to find common ground with the minority faction. Nonetheless, Brown and Clegg repeatedly attacked one another during the debates. Clegg’s recent warning only casts the prospect of an alliance in further doubt.