Yesterday when Nick Clegg announced that he would avenge David Cameron's decision to abandon the failed House of Lords Bill by voting against boundary reform, he set the tone for coalition politics in the months ahead. Whilst the last few months have hardly been harmonious for the coalition, the next few look set to be worse.

To those outside of the Westminster bubble, this spat will seem like a self-indulgent side show: I don't think I exaggerate when I say the public rarely cares about issues which involve politicians fighting politicians about electing other politicians. But make no mistake, this matters.

Boundary reform was a central plank of the Conservative re-election strategy and was estimated to deliver an extra 20 Conservative MPs at the next election. The fear amongst Conservative MPs and activists (myself included) is that it will now be difficult to find the extra votes needed to deliver a Conservative majority in 2015.

Managing party politics is always about balancing two often conflicting aims: doing what you want and doing what keeps you in Government. Conservatives have long complained that the Liberal Democrats are preventing them from delivering what they want, but have in general (Europe and House of Lords reform aside) accepted that continuing the coalition is still the best route to a Tory majority. But the danger for the coalition is that without boundary reform, MPs and activists will start to think the coalition is failing them on both counts. It's hard to keep a party happy that isn't getting what it wants now and fears it won't even get it in the future.

As Cameron cannot now point to boundary reform to show his backbenchers that he is leading them on the path towards a Conservative majority, it is likely that he will have to appease them by offering more Conservative policies. But with the Liberal Democrats unlikely to agree to a more right wing policy agenda, Cameron's room for manoeuvre is very small indeed.

Because of this, the coalition is set to face its biggest test. Will the Conservative parliamentary party be able to resist the urge to strike back at Clegg in retaliation for scrapping boundary reform? Will back bench Tories, for whom the prospects of a ministerial job are slim, be willing to follow the coalition script? Is it time for the coalition marriage to file for divorce?

The answer to the last question is not yet. Neither the Cameron nor Clegg would want to risk an election now with the Government suffering a particularly nasty bout of mid-term blues. But what we will see in the next few months will not be pretty. Rebellions are likely to increase, rows over policy will intensify and there will be a desperate scrabble for each coalition partner to assert their individual identity within the collective voice of coalition.

Clegg and Cameron still need each other, their fates are entwined with the deficit and the economy. Just don't expect them to be nice about it.

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