World News Today: Kennedy and Miliband put AV case

Postal vote being pushed into a letter box

The first UK-wide referendum since 1975 will take place on 5 May

Ed Miliband is to urge all "progressive forces" to come together to press for a new UK voting system as those seeking change launch their official campaign.

The Labour leader will join senior Lib Dem and Green Party figures in a cross-party push for a Yes vote in the 5 May referendum on the alternative vote.

But Lib Dem leader Nick Clegg, who also backs change, will not be at the event.

Meanwhile, four ex-foreign secretaries have said it would be a "grave error" to replace the system for electing MPs.

Voters will be asked on 5 May whether they want to keep the existing first-past-the-post system, where people select one candidate, or switch to the alternative vote where they are able to rank candidates in order of preference.

Mr Miliband, Lib Dem President Tim Farron, former Lib Dem leader Charles Kennedy and Green Party London Assembly member Darren Johnson are among those set to attend the launch of the official cross-party Yes to Fairer Votes campaign.

THE REFERENDUM CHOICE

At the moment MPs are elected by the first-past-the-post system, where the candidate getting the most votes in a constituency is elected.

On 5 May all registered UK voters will be able to vote Yes or No on whether to change the way MPs are elected to the alternative vote system.

Under the alternative vote system, voters rank candidates in their constituency in order of preference.

Anyone getting more than 50% of first-preference votes is elected.

If no-one gets 50% of votes, the candidate with the fewest votes is eliminated and their backers' second choices allocated to those remaining.

This process continues until one candidate has at least 50% of all votes in that round.

Q&A: alternative vote referendum AV poll: Where parties stand

But Lib Dem leader Nick Clegg is not expected to be present amid tensions between the deputy prime minister and senior Labour figures.

Mr Miliband has urged the Lib Dem leader to "lie low" on the issue and senior Labour figures have suggested his involvement in the campaign could threaten the chances of a yes victory given public anger with his party over student tuition fees and public sector cuts.

At Tuesday's event Mr Miliband will urge all those on the centre-left to unite behind the push for the alternative vote.

"The tragedy for progressive politics in Britain has been that division on the centre and left has handed a united right victory after victory," he is expected to say.

"For most of the last 80 years, there has been one Conservative Party - and others competing with Labour for progressive votes. The result, over the years, speak for themselves.

"No wonder the Tories back the current system. They know Britain is not a fundamentally Conservative country. But with first-past-the-post, they too often govern when progressive forces are divided. Britain deserves an electoral system that fairly reflects voters' views."

Launching their own cross-party campaign last month, the No to AV camp argued the alternative vote was a costly and complex system which could produce unfair results.

And, in a letter to the Times on Tuesday, four former foreign secretaries suggest that the principle of one person one vote in the current system was an example to other democracies.

"Those of us who have represented Britain internationally know one of the many reasons why we have always punched above our weight in the world is our simple and straightforward voting system, a system which everyone can understand," the signatories - including Margaret Beckett, Malcolm Rifkind, Lord Hurd, Lord Howe and current foreign secretary William Hague - argue.

"Today, billions of people elect their representatives through the system of one person, one vote... We believe it would be a grave error to abandon this principle."

While Conservative MPs largely support the status quo and Lib Dems back a switch to AV, Labour is divided on the issue with senior figures in each camp.

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