Without any fanfare or formal announcement, the government has moved into a new phase. ‘We’re not in a coalition now. We’re just cohabiting,’ says one Liberal Democrat. ‘We’re a sexless couple. We live in the same house but sleep in separate bedrooms.’

The two parties are governing together but pursuing increasingly separate agendas. As this Lib Dem source puts it, ‘They’re doing what they want and we’re doing what we want.’

This separation is a product of the fact that both sides want to fight the next election as distinct parties. This is particularly imperative for the Liberal Democrats. If they want to go into the 2015 campaign as potential partners for either major party, they can hardly synchronise policies with the Tories right up until next spring. So we’ll see the Liberal Democrats pushing for things they can claim as their own. Their aim for the next Budget, for instance, is to highlight their most popular policy by increasing the personal tax allowance still further, to £10,500.

The Lib Dems will ensure that their disagreements with the Tories are public and cast in emotive terms. Note how Clegg described George Osborne’s plans for more welfare cuts after the next election as a ‘monumental mistake’. This must be the first British government in which the rows in public are worse than the ones in private. Indeed, given the public criticism, relations are surprisingly cordial. I do understand, however, that Cameron and Clegg had a slightly rocky start to the year.

One thing that makes these Lib Dem jibes easier for the Tories to take is the knowledge that they appeal to left-wing voters who would otherwise plump for Labour. The Conservatives know that they can’t afford for the Lib Dem vote to collapse in Tory/Labour marginals. If an occasional bit of Lib Dem rudeness helps avert that nightmare, they can handle it. But one senior No. 10 source warns, ‘You cannot maintain long periods of slagging each other off.’

The Tories, meanwhile, are making their own efforts to distance themselves from coalition. Cameron used to wax lyrical about reforms the coalition was making which a single-party government wouldn’t have been able to. It sounded as if he genuinely believed coalition government to be more effective. But you won’t hear him talking like that any more. Partly, it’s because the coalition’s radical phase is now over. But it is also down to Lynton Crosby, the strategist Cameron hired to run the Tories’ election campaign. Crosby has made it clear that such language isn’t helpful if the Tories hope to win an outright majority.

The arrival of Crosby — who is based not in Downing Street but at Conservative campaign headquarters and doesn’t attend meetings with Liberal Democrats — has changed the focus of the Tories’ political thinking. Their time is now taken up less by potential deals in government and more by measures to maximise their vote at the next election. When Crosby arrived, he bluntly informed the Tory leadership that they couldn’t play for a draw and told them to put all thoughts of a second coalition out of their heads until after polling day.

Boris Johnson once remarked that the coalition was a triumph for the public school system. But now the privileged smoothness of the first few years has been replaced, on both sides, by a colonial toughness. Crosby, as you may have heard, is Australian, and the Lib Dem election campaign is in the hands of the South African Ryan Coetzee. Both have stiffened the sinews of their party leaderships and insist that party interest trumps coalition comity.

But the odd thing is that both sides know that they might well end up in government with each other again — and, as they draw up their manifestos, they are wrestling with exactly how to prepare for that eventuality.

The Liberal Democrats have settled for putting a few signature policies on the front of the manifesto and making clear that these will be their main demands in any coalition negotiation. But the Tory leadership is still debating what to do. Some favour keeping the manifesto as broad-brush as possible to maximise their room for manoeuvre in the event of another hung parliament. Others want as many specifics as possible, on the grounds that the more Tory policies there are, the more will make the agreement.

What’s certain is that the party leaders will come under pressure to set out their negotiating ‘red lines’ during the campaign. Cameron has already opened himself up to that, by promising that there will be an EU referendum if he remains Prime Minister, whether or not he’s leading a Tory majority. He is bound to be asked if the same terms apply to whatever other commitments he makes.

Cameron’s answers will be scrutinised closely by his own MPs. They know that if there is another hung parliament, they will be balloted on whether they want to go into coalition again. The result of any such vote is hard to predict. But I was struck when one high-flying minister told me that in a secret ballot, they would vote against a second deal with the Lib Dems. Their logic was that if the Tories were the largest party again, Cameron should ‘do a Harold Wilson’ and go back to the country to ask for an outright majority.

Even in Lib Dem circles, there is a recognition that it will be far harder to put together a coalition deal in 2015 than it was in 2010. Clegg’s confidants remain adamant that the party must nonetheless strike an agreement, whether with the Tories or Labour, though some senior figures in the party think that in a hung parliament the Liberal Democrats would be best served by wielding their power on a vote-by-vote basis.

One thing that seems an increasingly safe assumption is that this coalition will carry on until the election is called. Oddly enough, the move to ‘cohabitating’ makes that more likely. It gives the two parties the space they need to make their own arguments to voters. What the electorate makes of these arguments will determine whether another coalition is needed.