David Cameron says he will press ahead with a Commons vote on redrawing parliamentary boundaries, in spite of the prospect of Lib Dems joining with Labour to vote against it.
Deputy Prime Minister Nick Clegg has said that he will be ordering his MPs to oppose the changes after Tory backbenchers scuppered his plans to reform the House of Lords.
On a visit to an activity centre in mid-Wales, Mr Cameron insisted the changes would still be very much on the agenda when MPs come back to the Commons in the autumn.
He told reporters: "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.
He continued: "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 move will effectively put the Prime Minister on a collision course with Lib Dem ministers who are being urged to vote against their own Government.
Cutting the number of parliamentary seats and realigning boundaries to ensure roughly equal numbers of voters could give the Tories 20 extra seats at the next election.