Cameron: Labour 'opportunistic' in opposing AV vote
David Cameron has accused Labour of "opportunism" after the party said it would oppose a bill paving the way for a referendum on electoral reform.
Labour was the only party to include a referendum on changing to the Alternative Vote (AV) system in its general election manifesto.
But it has said it will oppose the coalition's referendum bill as it includes constituency boundary changes which it says help the Tories.
The referendum is scheduled for 5 May.
A referendum on ditching the current "first-past-the-post" format for Westminster elections in favour of AV was a key component of the coalition deal between the Conservatives and Lib Dems.
But it needs to get its Parliamentary Voting System and Constituencies Bill through Parliament to allow this to happen.
This is in some doubt, as Mr Cameron is facing unrest on the the Conservative back benches over the proposed date for the referendum, 5 May next year - the same day as elections to the Scottish Parliament, Welsh Assembly and Northern Ireland Assembly and councils in Northern Ireland and parts of England.
'Very, very partisan'
Labour says it is opposing the bill because it also contains proposals to shrink the number of MPs from 650 to 600 and to create constituencies of equal size across the UK.
This would benefit the Conservatives at the expense of Labour, as Tory-held seats on average contain more voters, meaning the party has to get more overall support to win as many seats as Labour.
But shadow justice secretary Jack Straw insisted on BBC Radio 4's Today programme that the difference was "marginal" and that the plans would abandon a "bipartisan" commitment to local inquiries adjudicating on disputes
He said: "If it had just been about the AV referendum, there would have been no difficulty in getting this bill through.
"What they have done is added to this bill their very, very partisan proposals effectively for gerrymandering boundaries.
"We are not arguing about the equalisation of seats. We are arguing about the unnecessary reduction in the size of the House of Commons and we are particularly arguing about the way in which they are proposing to go about redrawing the boundaries."
But Mr Cameron, who is on a trade mission to India, accused Labour of "a descent into complete and utter opportunism".
He told Today: "They are the one party who in their manifesto had a commitment to the AV referendum and they are now backtracking on that.
"I know what it is like in opposition. I did almost five years as leader of the opposition. The temptation to jump on the bandwagon and be opportunistic is always there and it should always be resisted."
Mr Cameron played down the significance of unrest on the Tory backbenches.
Some 43 Conservative and two Labour MPs have signed a Commons motion warning that holding the referendum on the same day as many elections risks distorting the result by inflating turn-out in areas where other polls are taking place.
But Mr Cameron said he was "confident" of getting the legislation through.
The Tories oppose bringing in AV, while the Lib Dems back it.
As part of the coalition agreement, the parties can campaign on opposite sides in the event of a referendum.
Mr Cameron said: "Obviously I understand and I share the views of all Conservatives who, by and large, don't want to see the AV system. We prefer the current system.
"But we entered a coalition where, in return for having a referendum on AV, we will have - which I think we need in this country - equally sized constituencies across the country and a smaller House of Commons."
Lib Dem deputy leader Simon Hughes accused Labour of "naked opportunism".
He added: "Each and every Labour MP campaigned on a manifesto committing to a referendum. Now they have the opportunity to make this happen but have chosen to say no for opposition's sake."
The AV system allows voters to rank candidates in their constituency in order of preference.
Anyone getting more than 50% of first-choice votes in the first round is elected, otherwise the candidate with the fewest votes is eliminated and their backers' second choices allocated to those remaining. This process continues until a winner emerges.
Ashley Dé, from the Electoral Reform Society, accused Labour and the Tory MPs signing the Commons motion on the timing of the referendum of being "mischief-makers".
It was "sabotage dressed up with a few principles", he added.
But Labour leadership contender Ed Miliband, who wrote Labour's election manifesto and backs a change to AV, accused Mr Cameron of striking "a shabby deal of convenience with the Liberal Democrats to rig the boundaries".
He claimed changing the boundaries would disenfranchise "millions" of people "who are predominantly poor, ethnic minorities and young" and was an "attempt to use the need for electoral reform as a cover for the low politics of gerrymandering".