Cameron will make clear he opposes vote system change

David Cameron will make it clear he opposes changing the voting system, in a referendum expected next May.

His spokesman said the PM would be asked his view and "clearly his view is that he's not in favour of it".

But the PM has said he will not play an active role in the "no" campaign.

The BBC understands a referendum is planned for 5 May 2011, if ministers can get it through Parliament, where many Tory and Labour MPs oppose it.

Opposite sides

It would mean the referendum is held on the same day as the Scottish parliament and Welsh assembly and English local elections.

It is understood a date for a referendum on changing from the current first-past-the-post system to the alternative vote (AV) will be confirmed at a cabinet meeting next Tuesday.

It may seem odd that the date of 5 May should be so crucial - but for Nick Clegg it is a major victory.

It significantly strengthens his own position and the prospects for the coalition holding together.

The great fear in Lib Dem circles was that the AV referendum would be booted off into the long grass by a Conservative Party that regards voting reform as an unwelcome distraction.

A vote on 5 May gives Lib Dems certainty - a definite timescale for achieving what most regard as the single most important concession wrung out of David Cameron in the coalition agreement.

The hope too is that, because 5 May coincides with local, Scottish and Welsh elections, it will boost the chances of a "yes" vote by bolstering turnout.

It also gives Nick Clegg the opportunity to campaign against the Conservatives and so underline his party's independence and demonstrate to anxious supporters that it has not become an annexe of the Conservative Party.

Mr Cameron has said he is opposed to AV in the past. But his spokesman said on Friday that a commitment to holding a referendum on changing the voting system was "central to the coalition government's programme".

He said a statement from Mr Clegg on the topic was anticipated but he did not confirm the referendum date.

A change to the voting system is opposed by the Conservatives but was promised to the Liberal Democrats as part of the coalition deal.

They agreed to whip their parties into supporting the referendum, but allow them to campaign on opposite sides during the campaign.

The Tories say the existing first-past-the-post system guarantees strong, stable government, while Lib Dems argue it is unfair on smaller parties and allows candidates to be elected on the support of only a minority of constituents.

Under the proposed AV system, voters rank candidates in order of preference and anyone getting more than 50% in the first round is elected.

If that does not happen, the candidate with the fewest votes is eliminated and voters' second choices allocated to the remaining candidates. This process continues until a winner emerges.

The Lib Dems themselves would prefer a different vote system - the Single Transferable Vote - a more proportional system than AV.

Speaking before the general election, Lib Dem Deputy PM Nick Clegg told the Independent: "AV is a baby step in the right direction - only because nothing can be worse than the status quo."

'Great sway'

Conservative MP Daniel Kawczynski, chairman of the all-party group for the promotion of first-past-the-post, said he was very concerned about AV which he said would create "two classes of voters" - and said he would campaign "vigorously" against it.

But he said he would not vote against a Bill setting up a referendum although he would "love" David Cameron to campaign against AV in the build-up to the vote.

Mr Kawczynski added: "I think he would hold great sway in such a referendum."

It is not my party's job to prop up the Liberal Democrats by helping them win a referendum that is important to them

Campaign group the Electoral Reform Society welcomed the news as "a real chance for change".

It is thought the referendum will be linked to plans to change constituency boundaries - a key concern of the Conservatives but something fiercely opposed by Labour.

The Tories pledged to make constituency sizes more "equal" in their manifesto - Labour say the plans are designed to eliminate smaller inner-city seats which they hold.

The previous Labour government also promised a referendum on the AV system.

Shadow foreign secretary David Miliband told the BBC that if he won the Labour leadership contest, he would back a referendum and allow activists to campaign in favour of a switch to AV.

His brother Ed, another leadership candidate, also said he "strongly" supported the case for introducing AV "to ensure greater fairness for voters and greater legitimacy for our MPs".

But another leadership candidate, shadow health secretary Andy Burnham, told the Guardian: "It is not my party's job to prop up the Liberal Democrats by helping them win a referendum that is important to them."

And leadership rival Ed Balls said that while he supported AV, he was concerned that the government was "choosing to push this through" alongside constituency boundary changes which he said amounted to a "gerrymandering of our political system".