From left to right, in more ways than one: Boles, Letwin and Maude; Pritchard, Montgomerie and Fox

EVEN before last May, Britain did have political coalitions of a sort. The main parties have themselves always been uneasy alliances. The Liberal Democrats, born of the old Liberals and the more left-wing Social Democrats, are the most obviously divided. Labour often struggles to reconcile the cultural conservatism of its working-class heartlands with the liberal instincts of its metropolitan supporters.

Margaret Thatcher and John Major, the two previous Conservative prime ministers, can bitterly attest to the fractiousness of the Tories, too. The splits under their successor, David Cameron, are small in comparison—but they are widening. The party's right grumbles about the prime minister's policy sops to his Lib Dem coalition partners. The left provocatively suggests an electoral pact with them.

The Tories' half-hearted campaign in the Oldham East and Saddleworth by-election (held on January 13th, as The Economist went to press), implicitly intended to boost the Lib Dems, angered the party's right. Mr Cameron is likely to do even more to compensate the Lib Dems for the crushing losses they are expected to suffer in May's local elections, a possible “no” vote in a referendum on voting reform and other impending traumas. The antagonism between Tory left and right could be one of the main political themes of the year.

But who are these squabbling tribes? Though they crave lower taxes, the modern Tory right—embodied by Liam Fox, the defence secretary, Tim Montgomerie, an influential blogger whose distinction between “mainstream” and “liberal” Conservatives is catching on, and backbenchers such as Mark Pritchard and Bernard Jenkin—are not as preoccupied with economics as the “dry” Thatcherites of yesteryear. If they were, the government's ferocious spending cuts would keep them happy.

Culture and home affairs matter just as much. The government's liberal noises on crime and counter-terrorism have aroused more anger on the right than its retention of the 50p top rate of income tax. The right resents austerity when it is applied to defence; it wants Mr Cameron to revive his former reverence for the family. Its adherents are at pains to describe themselves as conservatives rather than libertarians. Some old Thatcherites, having read their Hayek, would have drawn the distinction in just the opposite way. The strongest bond between the old right of the 1980s and 1990s and the new version is another non-economic cause: Euroscepticism. On January 11th 27 Tory MPs voted for an amendment to toughen up the government's European Union bill.

The new Tory left is, if anything, even further removed from its antecedents in previous decades. The “wets” of the Thatcher era, such as Ian Gilmour and Douglas Hurd, were in a sense more conservative than their right-wing adversaries. They feared Thatcherism was too big a shock to the British system and trusted in the wisdom of Westminster and Whitehall. They tended to side with the established consensus: they shared the pragmatic pro-Europeanism of the diplomatic elite and the Home Office's pessimism that little could be done about rising crime.

By contrast, the new left—including the Cabinet Office ministers Oliver Letwin and Francis Maude, and the backbencher Nick Boles—are iconoclasts who define themselves by their zeal for giving power away. They have diverse views on economics, crime and Europe, but share a commitment to stronger local government and more control for ordinary people over public services. They admire the Lib Dems for their centrifugal instincts.

There are still plenty of heirs to the old-left tradition in the party: ministers such as Damian Green and (at least on issues pertaining to his justice brief) Ken Clarke; august backbenchers such as Tim Yeo and Andrew Tyrie. But the new left is now more influential. Running parallel to the coalition's austerity programme is a bold plan for decentralisation: more elected city mayors, more people power in areas such as education, the NHS and policing, and unprecedented transparency and openness in the state. Such irreverence towards the commanding heights of government would shock old wets.

Big Society, big tent

The new shape and character of Tory divisions actually helps Mr Cameron in some ways. Because the right is now as cultural as it is economic, and the left more enthusiastic about decentralising power, both can rally around Mr Cameron's idea of the “Big Society”. This vision of a more communitarian conservatism has always had far more followers on the Tory right than is often assumed. In opposition, Mr Cameron's most metropolitan advisers built surprisingly good relations with Christian conservatives. Both sides were passionate about reviving civil society.

But there are problems for the prime minister, too. The bitterest row between left and right dates back to the last election, which led to the formation of the coalition. Those on the right say Mr Cameron fluffed an eminently winnable contest by relying on a clique of aloof and overconfident advisers, whose campaign strategy ignored popular themes such as immigration. Those on the left say the election result was proof that the party had not ditched enough of its right-wing baggage.

Both sides have a point; but the right's anger is more intense. It already regards George Osborne, the chancellor of the exchequer, as the real guardian of the Tory interest in the coalition. The downside of Mr Cameron's vast self-belief is complacency, often manifested in an inattentiveness to his own political backyard. If he needs the support of his right flank in a future crisis, he cannot be sure of getting it.