LONDON - Opposition Liberal Democrat leader Nick Clegg appealed Saturday for an overhaul of British politics, saying he wanted changes to an electoral system that has kept the country's Labour and Conservative parties in power for generations.

Clegg's perennially No. 3 party has done spectacularly well in the polls, throwing the British electoral contest wide open in one of the most exciting races in decades. But even with a surge in support, Clegg is still not expected to capture enough seats in the May 6 election to win a majority in Parliament, and speculation has centered on who Clegg might choose to form a coalition.

The party leader said his focus was on electoral reform, and proceeded to talk up the gulf between himself and Tory leader David Cameron, who has resisted such change.

"There's such momentum behind the reforms we're talking about," Clegg told The Associated Press during an interview aboard his campaign bus as it traveled through southwest England and Wales. "That momentum becomes unstoppable. I personally don't think that any politician after the election can deny the case for very extensive political reform. I'm amazed David Cameron is choosing to do so."

Clegg wants a change to Britain's "first past the post" voting system, in which candidates need the highest number of votes - rather than an absolute majority - to win a seat in Parliament. The system has tended to stack the electoral math in favor of Prime Minister Gordon Brown's Labour Party, which enjoys broad support across Britain, at the expense of the Liberal Democrats and Tories, whose support is more uneven.

Many analysts have said that Clegg would demand the system be overhauled in return for any help forming a coalition government.

Cameron has dismissed the idea of reform, calling the proportional representation demanded by the Liberal Democrats a "great con" that would lead to coalition governments hammering out policy in back room deals.

Cameron has little choice but to resist reform, said Bill Jones, a professor of politics at Liverpool Hope University.

Allowing proportional representation would open the door to a center-left coalition of Labour and the Liberal Democrats, which would crowd the Tories out of power - perhaps for several election cycles to come.

"It would mean signing their own death warrant," Jones said.

Clegg's criticisms of the Tory leader come on the back on an interview in The Guardian newspaper in which Clegg said there was "a gulf in values between myself and David Cameron."

"They have no progressive reform agenda at all, only an unbearable sense of entitlement that it's just their time to govern," the left-leaning publication quoted him as saying.