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British voters must decide whether to ditch decades of ballot box tradition, or go Hollywood in parliamentary elections by adopting the same voting method used for the Academy Awards.

The campaign ahead of Thursday's national referendum has elements of a blockbuster: sworn political foes banding together, stormy bust-ups across the Cabinet table, rising tensions in the country's most important bromance — the alliance between Prime Minister David Cameron and his deputy Nick Clegg.

Offering voters a chance to usher in electoral reform is a long-held ambition of Clegg's Liberal Democrats — who joined with Cameron's larger Conservative Party in Britain's first governing coalition since World War II following last year's inconclusive national election.

A change to Alternative Voting — AV — would generally favor the Liberal Democrats, the perpetual third-place party, while usually reducing the number of seats won by the biggest parties, the Conservatives and Labour.

Britain currently uses a first-past-the-post system, under which the candidate with the most votes — not necessarily an absolute majority — wins a seat in the House of Commons.

Under proposals being put to voters, Britain would switch to a system which asks electors to rank candidates in preference order.

If no candidate clears 50 percent of first choice votes, the last-place candidate is eliminated and the second choices of his or her supporters are distributed. The process continues until one candidate clears the 50 percent bar.

Clegg insists the reform is vital to restore trust in politics following a damaging 2009 scandal over lawmakers' wild expense claims. Cameron opposes any change, and some analysts wonder whether their coalition can withstand the fallout from this week's vote.

Opponents of the current system — including Clegg and Ed Miliband, leader of the main opposition Labour Party — argue that the current system is unfair, particularly in a country where voters are increasingly likely to cast votes for smaller parties and poll results are less clear cut.

In Britain's national election last year, the Conservatives who now lead the government got 36 percent of the vote but 47 percent of the seats in the House of Commons. The Liberal Democrats got 23 percent of the votes but 9 percent of the seats, while Labour won nearly 40 percent of seats with 29 percent of the vote.

In the 1950s, more than 95 percent of votes were cast for the Conservatives and Labour. Last year, 35 percent of electors offered support for parties other than the two main contenders.

AV is used in parliamentary elections in Australia, Fiji and Papua New Guinea, in Ireland for elections to select the country's president, and perhaps most famously to pick winners of the Oscars.

Advocates claim that under the present system too many lawmakers are elected with the support of less than half of people in their district, and few districts change hands, encouraging legislators to become complacent.

"Candidates will need to knock on more doors, make more phone calls and listen more carefully to those who disagree," said Ed Miliband, leader of the main opposition Labour Party. He has campaigned for AV, but the reform is controversial within Labour as well and Miliband allowed others in his party to campaign against it.

Opponents say the proposed new system is overly complex and would lead to murky backroom deals to form governments. They fear weak leadership under unwieldy coalitions, as opposed to one dominant party calling the shots.

Foreign Secretary William Hague, who opposes any change, said 200 years of hard-won electoral reforms had produced the first-past-the-post system — also used in about 50 other countries, and much of the United States.

The alternative vote system "does not represent electoral reform, but a damaged democracy that nobody wants," Hague said. "The world would be baffled by it, and rightly so."

The campaign has offered the unusual sight of once bitter rivals like Labour's combative ex-Home Secretary John Reid and Cameron sharing not just the stage, but the same argument.

Tensions have seen coalition colleagues clash — with Climate Change Secretary Chris Huhne, a Liberal Democrat, threatening Conservative ministers with legal action, and angrily interrupting a Cabinet meeting to complain to Cameron.

The vote on Thursday — which takes place alongside elections for English townhalls and assemblies in Scotland, Wales and Northern Ireland — is Britain's first national referendum since a 1975 ballot on whether or not to remain a member of Europe's economic bloc.

Though it promises the most radical change to the voting system since women won the right to vote in 1928, many members of the public are unmoved, or simply confused.

"I'll vote," said Clara Lloyd, a 32-year-old social worker from Machynlleth, Wales. "But without really knowing what I am voting for."

Some suggest the clamor for political change of a year ago has abated, replaced by public dissent to the coalition's plans for harsh spending cuts. Polls ahead of the vote show few people say they are certain to cast a vote, but that retaining the status quo is the likeliest outcome.

Anger over the program has spilled into violent street protests in central London — and some may oppose the change simply because it has been advocated by Clegg, who is derided for endorsing Cameron's austerity measures and breaking a promise not to increase college tuition fees.

The ballots vote's also been overshadowed by a moment that transfixed the British public — the royal wedding. Victoria Hawkes, a 31-year-old physiotherapy assistant from Tamworth, in central England, also had events in her own life to worry about.

"I've been busy with other things. I just got married last weekend, and haven't really paid attention," she said.

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Caroline Morrow in London contributed to this report

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David Stringer can be reached at http://twitter.com/david_stringer