Media playback is unsupported on your device Media caption Labour launches two AV campaigns: Ed Miliband and Caroline Flint set out their views

Ed Miliband has said those in his party campaigning against the Alternative Vote are "wrong" as he launched Labour's "Yes to AV" campaign.

As more than 200 of his own MPs and peers came out against changing the UK voting system, Mr Miliband said he respected them, but disagreed.

He said he believed AV was "fairer" and Westminster's political system had been "stuck in neutral for too long".

Three shadow cabinet members are among Labour figures opposing AV.

Voters will be asked whether they want to keep first-past-the-post or switch to the Alternative Vote on 5 May.

All registered UK voters will be entitled to take part in the referendum, in which they will be able to vote - by putting a cross in a box on the ballot paper - yes or no to changing the way MPs are elected. Whichever side gets the most votes will win.

Mr Miliband supports AV - where voters can rank candidates in order of preference - but has said Labour MPs and peers are free to take their own view.

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. Referendum views: Yes campaign Referendum views: No campaign

However, his party is increasingly split on the issue, with more than 20 frontbenchers, as well as senior figures including David Blunkett and Lord Prescott, against change.

At the launch of Labour's yes to AV campaign, Mr Miliband said: "I respect those in our party who are against change but I think they are wrong and I disagree with them."

Former leader, Lord Kinnock, former Home Secretary Alan Johnson and former mayor of London Ken Livingstone were among those at the launch of the "yes" campaign.

In his speech, Mr Miliband said Labour had to "take a stand on this issue".

"These opportunities don't come along very often, and we've got to seize that moment, in my view."

He said people saw Westminster as "remote and out of touch", membership of political parties had declined and AV could help "change our politics".

"By having more votes counted as part of our system it will mean that politicians take more voters seriously, it will encourage candidates to appeal to a broader range of voters and to understand a wider range of concerns."

He said it would "open up the electoral battleground" and people should ask themselves if they were happy with the condition of British politics.

"If the answer is no, then people should seize this moment for change."

He urged Labour supporters to ignore the temptation to vote "no" in order to damage Deputy Prime Minister and Lib Dem leader Nick Clegg, who is also campaigning for AV.

He said voters hated it when politicians exaggerated their differences and argued that the Alternative Vote would make Labour more likely to be "open and straight" about what it thought of other parties.

Senior frontbenchers, including Ed Balls, Douglas Alexander and Tessa Jowell, support a switch to AV, as does David Miliband.

But more than 200 Labour MPs and peers have come out in support of the "Labour No to AV" campaign - including three members of Mr Miliband's own shadow cabinet, John Healey, Caroline Flint and Mary Creagh.

Another 19 members of Labour's frontbench are also opposing Mr Miliband on the issue.

Writing in The Independent, John Healey - the shadow health secretary - said AV was not an improvement on the current system and would make the Lib Dems the "kingmakers" in a likely hung Parliament.

"The last thing we should do is throw away what works in favour of an unfair, perverse electoral system," he wrote. "Politicians should be seeking the trust of voters not encouraging them to move the goalposts."

Labour peer Lord Falconer suggested that Mr Miliband could delay his chance of becoming prime minister if the yes campaign is successful.

He told the New Statesman magazine that it would mean the Lib Dems would want to delay the general election until 2015 when AV would be introduced.

"But if the Lib Dems lose the referendum, there will be no reason to delay - the quicker they get out of the coalition, the sooner they will be on the road to recovery with the electorate," he said.

The AV referendum was a key coalition agreement between the Lib Dems, who want to change the voting system, and the Conservatives, who want to keep first-past-the-post.

Prime Minister David Cameron is campaigning for the status quo.