Boundary changes analysis: A day of twisted coalition spite and bile

As I write this, voting is underway in the Commons chamber. Lib Dem ministers are, for the first time, voting against their Conservative colleagues in government. Some will feel a strange sense of exhilaration as they do so. They're making a mistake: this is bad news for both parties.

For too long the Lib Dems have been sidelined, ignored, abused by their Tory colleagues. They were handled with contempt by the Conservatives during the electoral reform referendum. They have been trampled on by a media confused and unyielding to the realities of coalition politics. This sort of treatment was nothing new to British politics' third party, whose very existence has puzzled all other political activists and created a very thick skin among its own.

The problem was this pugnacious anti-establishment 'otherness' eventually led to trouble. Clegg, probably the most despised mainstream politician of the 2010s, personifies the Lib Dem thick-skinned mindset. It was his bombastic handling of Lords reform proposals which led to their downfall. The plans were too inflexible, too brazen, to succeed. Liberal Democrats blame the Tories for resisting, but they should blame themselves, too. Constitutional reform is a long game: the Lib Dems overreached, seeking more than was achievable, and paid the price.

Now their bitterness is making the Conservatives pay the price, too. With the next general election likely to yield a hung parliament, Cameron would have needed every one of the 20 extra MPs these boundary changes would have brought him. Following today's defeat, his chances of winning that overall majority are reduced drastically. Those backbenchers who brought down Lords reform last year could have a heavy responsibility to bear. The ultimate result of the Lords reform defeat could be the Tories find themselves forced to talk to the Lib Dems about reviving their coalition for another five years.

Given the likely collapse of Lib Dem MPs after 2015 as a result of the Tory-dominated government this time round, the parliamentary arithmetic could make even that possibility unfeasible.

If that's the case the Tories may find themselves obliged to govern as a minority. Clinging on by brokering deals with the minority parties – the nationalists and the Northern Ireland MPs on the big crunch votes – doesn't sound like much fun. With the Lib Dems voting against them this afternoon, the Tories had no choice but to try and reach deals. They were reportedly rebuffed, despite having made tempting offers. The Conservatives have learned how unpleasant the alternative is – but too late to change the ultimate fate of this government's constitutional reform car crash.

There is a strong whiff of the Lib Dems doing everything they can to bring the Tories down with them. For, despite the grim satisfaction they are taking in making a stand, they will pay a heavy price themselves for the infighting it has triggered. Conservatives will point out they have voted for cuts to public services, but not cuts to the number of MPs. Another part of Clegg's constitutional reform agenda has bitten the dust. Worst of all, every negative headline undermines the impression that the great coalition experiment has failed.

Labour knows all this. The opposition is reaping the harvest from its preposterous Lords reform positioning last year. It was Ed Miliband who made the Tory rebellion possible, by arguing he supported an elected second chamber in principle but making it impossible to achieve. Now that superb piece of positioning has proved more effective than any single win in prime minister's questions. The boundary changes defeat matters far more to the outcome of the next election than even the coalition's biggest U-turn, or the resignation of a Cabinet minister. The opposition's strategists will be delighted at how this has panned out.

Voters might be delighted that the negative aspects of the boundary review will not now become reality. The arbitrary way in which the boundary commissioners were forced to ignore community ties, to keep to the rigid guidelines demanded by the government's rules, will not now go ahead. Many, though, will remain in the same old safe seats which have not changed hands for years. Britain's current electoral system means voters in marginal seats are the ones which decide the election. For many millions of people supposed to elect MPs to the mother of parliaments, their vote will be as irrelevant as ever.