Nick Clegg is battling to prevent Conservative reprisals after leading his MPs to vote with Labour for the first time since the coalition was formed, in order to defer the parliamentary constituency boundary review until after the next election.
The delay passed by a margin of 334 to 292, severely damaging David Cameron's chances of winning an overall majority at the next election. It is likely to be taken as a sign that his political team has been badly outmanoeuvred by Clegg. It is the first time that Liberal Democrat ministers in the Commons have voted against the Conservatives on a piece of coalition legislation.
The move means Cameron will have to abandon his dual plan to cut the number of MPs to 600 and fight the next election on redrawn boundaries designed to equalise the number of voters in each constituency. In some cases, due to demographic change, constituencies will be as small as 60,000 electors, and others will be well over 80,000, a disparity that Clegg condemns in principle.
The vote followed a bitter debate in which angry backbench Tory MPs repeatedly rounded on Liberal Democrats for backtracking on a commitment to a boundary review before the election.
But Clegg is now anxious to limit the damage to the coalition, and not set off a further chain reaction of reprisals in which the Tories respond by in turn tearing up another section of the coalition agreement.
The coalition has a series of difficult issues ahead on childcare funding, securing growth, bank reform and press regulation. The signs are that Cameron will treat the issue as a self-contained event.
Clegg insists he was forced to act after Cameron admitted last summer he could not deliver enough of his own backbenchers to vote for an elected second chamber.
Clegg had at the time warned Cameron he would respond by rejecting the boundary review if the Tories blocked his single most important item of political reform. The Tories countered there had never been any linkage between the two issues in the coalition agreement.
Senior Liberal Democrats and Labour whips were worried about Tuesday's vote, sensing that Cameron would be desperate to win, but in the end he had nothing to offer. He also suffered a small backbench rebellion of his own MPs voting against him, led by David Davis, the senior rightwing backbencher.
Cameron himself held talks with some nationalists in a bid to persuade them to let the boundary review go through, but the Democratic Unionists feared the review would weaken their chances of winning seats not just at Westminster, but also the Northern Ireland Assembly. The SNP MP Pete Wishart insisted "accusations that the SNP were working for a deal with the Tories to hinder Scottish Labour are ludicrous. We had no intention of supporting the Conservatives in any vote on the boundaries plan and no discussions took place."
In a bid to lower the temperature Clegg stayed away from the debate and let a backbencher, John Thurso, make the case for delay.
But the Tory MP Penny Mordaunt said the Lib Dems were motivated by "spite, pettiness and self-interest" and were making "flirtatious glances" to Labour as potential coalition partners following the 2015 poll.
"The Liberals have exchanged their legendary sandals for flip-flops in the hope that it will enable them to keep their options open," she said. She added the Liberal Democrats had tainted politics.
Tory backbencher Peter Bone said Liberal Democrat ministers voting against the Conservatives would if they had any principle resign since they could not accept collective responsibility.
Experts calculate the 2010 election fought on the redrawn boundaries would have resulted in the Tories just securing an overall majority, with Labour down 36 seats and the Liberal Democrats down six.
Anthony Wells, the polling expert from YouGov, has calculated that on current boundaries the Conservatives need a lead of 11.1% to win an overall majority on a uniform swing. They also need a lead of 4.1% to be the largest party.
On the revised boundaries the Conservatives would need a lead of 7% to win an overall majority and would need a lead of 1.4% to be the biggest party.
guardian.co.uk © Guardian News and Media Limited 2010
image: © Liberal Democrats