David Cameron has set himself on a collision course with Nick Clegg by challenging Liberal Democrat ministers to vote against the coalition government after he said he intended to press ahead with plans to redraw the electoral map.
Yesterday Nick Clegg said his party would vote against the boundary review when it came to a vote in mid-2013 after Tory MPs blocked Lib Dem backed plans to reform the House of Lords.
The change to the constituency boundaries that cuts the number of MPs from 650 to 600 would provide a much needed boost to the Conservative's chances of winning an overall majority at the next election.
Speaking during a visit to Wales on Tuesday, the prime minister said: "We want the boundary change vote to go ahead."
"I am going to be saying to every MP 'Look, the House of Commons ought to be smaller, it ought to be less expensive and we ought to have seats that are exactly the same size'," he said.
"I think everyone should come forward and vote for that proposal because it is a very sensible proposal and it will be put forward."
Labour has said the boundary changes are "gerrymandering" designed to tilt elections in favour of the Tories, and is expected to vote against them.
In order for the review to be defeated Lib Dem ministers as well as backbench MPs would have to join Labour in opposing the changes.
This could provoke a crisis in the coalition as ministers are expected to vote in favour of government measures and usually would be fired or asked to resign if they did not.
However under the terms of the coalition agreement no Liberal Democrat minister can be removed by the prime minister without "full consultation" with the deputy prime minister.
On Monday Clegg said he would tell his MPs to vote against the boundary review as the Conservatives had "broken" the coalition contract by killing plans to create an elected House of Lords.
"I cannot permit a situation where Conservative rebels can pick and choose the parts of the contract they like, while Liberal Democrat MPs are bound to the entire agreement," he said.
Clegg's threat that the Lib Dems will vote down the boundary review has been met with outrage by many Tories, who argue the two policies should not be linked. They say that the boundary review was what their party got in exchange for agreeing to hold the AV referendum.
Lewis Baston, a senior research fellow at the think-tank Democratic Audit, told The Huffington Post yesterday if the Tories fail to secure a reduction in the number of MPs, the keys to Downing Street could be handed to Ed Miliband.
"Fighting the next election on the same boundaries as last time will increase the probability that the election will result in another hung parliament, probably with Labour as the largest single party," he said.
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