David Cameron says he will press ahead with a vote next year on constituency boundary changes that will benefit his party at the next election, even though Nick Clegg has said he will instruct Liberal Democrat MPs to vote down the measures.
Cameron said: "I am going to say to every MP: 'Look, the House of Commons ought to be smaller, less expensive and we ought to have seats which are exactly the same size'.
"I think everyone should come forward and vote for that proposal because it is a very sensible proposal and it will be put forward."
The prime minister would not be drawn on whether Liberal Democrat ministers would be deemed to be in breach of the ministerial code if they voted against government measures, but if he were to make such a ruling, he would in effect be spelling the end of the coalition.
The vote is due next autumn and is bound to become a political flashpoint. Cameron will be put under some pressure from the Tory right to face down the Liberal Democrats, and threaten an early general election from which Clegg's party is unlikely to benefit.
The alternative would be to end the coalition and run as a minority administration, but press the Liberal Democrats to vote on individual measures, a system known as confidence and supply.
It is more likely that Cameron will have to accept that the Liberal Democrats are not going to vote through the boundary changes, and carry on with the coalition.
The issue of the equalisation of the electorates of parliamentary constituencies is not likely to be seen as a sufficient reason to end the coalition, especially since the task of reducing the deficit will be only half complete.
It is almost impossible for Cameron to win the boundary review vote in either the Commons or the Lords without the support of the Liberal Democrats since Labour and the minority parties are opposed to the way the reform has been implemented. Some Tories fear that without the boundary changes securing an overall Conservative majority at the 2015 general election would become virtually impossible.
Cameron said he was frustrated by the inability to get Lords reform through parliament, and said the right response was to focus on the economy in the near future.
There is no agreement between the two parties on how to fill the vacuum in the parliamentary programme created by the abandonment of Lords reform. It is likely to be resolved in September when parliament reconvenes briefly ahead of the party conferences.
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