Image caption Not all Australians are surfers - but all have to vote

As Britain decides whether to change the way MPs are elected, can we learn anything from Australia, the only major democracy that uses the method on offer? The BBC's Rebecca Keating, an Australian herself, explains how elections work Down Under.

There is a carnival-like atmosphere on polling day in Australia.

Bunting in party colours adorns the fences of schools that serve as polling stations, and activists throng the gates jostling to hand out their how-to-vote cards.

Voters, compelled by law to cast their ballot, refresh themselves at the sausage sizzle or try their luck in the school's fundraising raffle.

And, since 1918, in the little privacy the cardboard polling booths allow, they choose their governments using the alternative vote.

Australia is the only major democracy in the world to use the alternative vote for elections and across the country there are several variations.

For state elections in Queensland and New South Wales, voters use a form known as 'optional preferential voting' - the same system Britain would adopt if voters say "yes" to 5 May's referendum question.

Under this system, voters can rank one, some or all of the candidates on the ballot paper in order of preference.

The first preference votes are counted and if no candidate has secured 50% of the vote plus one, the candidate with the lowest number of votes is eliminated.

Impact

The second preferences of that candidate's supporters are then distributed. This goes on until one candidate reaches an absolute majority.

Image caption Candidates are ranked in order of preference

According to those campaigning for a Yes vote in 5 May's referendum, introducing the alternative vote to UK general elections would eliminate safe seats and force MPs to work harder to woo their constituents.

Australian elections expert Antony Green says the Antipodean experience shows that in most cases using the alternative vote to elect a candidate delivers the same result as the first past the post system.

"It only really has an impact in contests where the leading candidate has well below 50% of the votes," he said.

Mr Green says it is unusual for the outcome of more than 5% of contests to be changed by the distribution of preferences and cites the New South Wales election held in March.

"There was only one seat out of 99 where the result was changed from first past the post," he said.

"The Liberal Party led the field with 32% of the vote in one electorate. The Labor Party and the Greens were just under 31% behind.

"The preferences flowed strongly between Labor and the Greens and the Liberal Party was defeated by the second-running Green candidate."

Extremist parties

The 'No' campaign argues this quirk of the alternative vote would favour extremist candidates, who could be behind in the early rounds of counting but win when preferences are distributed.

Mr Green says smaller parties may experience a surge in support on first preferences but will struggle to gain seats.

It's not an issue because we've had our system for so long. It's not going to change John Howard, Former Liberal Prime Minister

"The experience of parties in Australia like One Nation or the Communist Party is that they often would poll well but under AV they have no hope of getting elected because they are run down on preferences," he said.

"It's harder for a minority party or an extremist party to get elected because they need the majority of the vote."

The quest for a majority is where the Australian tradition of how-to-vote cards - a method of tactical voting decided by party leaders - arose.

Voters entering polling stations run the gauntlet of activists brandishing these cards, which tell people how to allocate their preferences so allied parties benefit if their number one candidate is eliminated.

They can choose to accept these suggestions or number the ballot their own way.

Image caption Most Australian voters have never used anything but the alternative vote method

Mr Green says in some contests, preference deals like these would see parties talking to others on their side of politics in a more conciliatory way.

"At the moment the tactical voting strategy in the UK is telling people not to vote for a small party and split the vote," he said.

"That doesn't apply any more and parties will have to appeal beyond their own supporters.

"For example, Conservatives might talk to UKIP candidates and get better relations with those."

Hankering for change?

For all the barbecues and bonhomie on election days Down Under, 'No' campaigners have suggested Australians have a hankering to abandon the alternative vote.

A poll conducted for the Institute of Public Affairs late last year found 57% of voters preferred first past the post and 37% supported the current Australian system.

Tony Barry, a research fellow at the institute, said it showed "people are not satisfied with the status quo" and some sort of reform was needed.

But former Liberal Prime Minister John Howard senses no mood for change.

"It's not an issue because we've had our system for so long. It's not going to change," he said.

Britain decides if it will change how it elects its members of Parliament on 5 May.

The experience of Australian voters suggests that whatever the outcome of the referendum, the outcome of future elections is likely to be largely unchanged.