Sean O'Grady: Pragmatism will hold Osborne and Cable together

For months and years the coalitionists will face the wrath of disillusioned voters

When will he coalition's honeymoon end? On 25 June. That is the date pencilled in, 50 days after the general election, when George Osborne will present the emergency Budget that he promised will set the framework for the restoration of the public finances.

At that point the Con-Lib deal will face its first real test. The reality of immediate cuts in public spending will become apparent, and the left-radical wing of the Liberal Democrats will be asked to stretch their loyalty to Nick Clegg still further.

It is difficult to imagine the Lib Dem rebels – and there will be some – pushing things so far as to threaten the life of the coalition in its very infancy, but their resistance to Toryism is deep, especially in the South-west and Scotland. Nick Clegg said in his joint press conference that, until a few days ago, he and David Cameron had been "rivals" – but "enemies" would be more accurate. The late-night scrambles for votes in the Commons as the whips struggle to hold together this odd coupling, and the open hostility of many Lib Dems in the country, will demonstrate that ideological fissures have not been healed by the Clegg-Cameron bonhomie and the businesslike language about cutting the deficit. So will the votes at Lib Dem conference condemning this or that coalition policy, and the shrill voice of the Tory right will join the discordant chorus. It would be no great surprise if, in such a febrile atmosphere, many Lib Dems heeded David Miliband's call for the progressive forces to regroup.

By the autumn, Liberal Democrat and Conservative MPs will be faced with a new comprehensive spending review – and the nation will wake up to its long-postponed living nightmare of huge, specific, explicit cuts in public services. These they will expected to go back to their constituencies and defend. The pain will be prolonged – for months and years the coalitionists will face the wrath of disillusioned voters as they watch local libraries shut, social services slashed, rail services cut and schools go without.

But the leadership of the coalition ought to hold: purely on pragmatic economic grounds, Vince Cable and David Laws' instincts are the same as George Osborne's more ideological ones. The tensions will be more personal, perhaps. Vince Cable may find it difficult to relinquish his habitual role as the alternative, chancellor-in-waiting, especially when many in his own party, and even Mr Osborne's, may wonder why the more competent economic figure has been given the lesser job. Mr Cable may continue to upstage his younger Tory colleagues in the media. Mr Laws meanwhile, as Chief Secretary to the Treasury, seems destined to be the man who does the coalition's dirty work.

"Strong and stable" government is the ambition of what we may call the CCC (Cameron-Clegg Coalition) for short; but the habitual oppositionism of the Lib Dems may undermine that. This is truly uncharted territory; the first coalition since 1945, and the toughest spending cuts since the 1970s, if not the Second World War. It would be a stressful experience for even one-party government; for a fragile partnership it will be still more traumatic.

There is another factor, too. The logic and momentum of the Westminster system – collective cabinet responsibility, the stark division between Government and Opposition, the way Lib Dems will have to defend Conservative ministers and vice-versa; all this will inevitably draw some elements in both parties closer together. But the more fundamentalist, tribal Liberal Democrats will find the same process repelling them. How can they fight a by-election against each other?

British political culture, in other words, forces the Lib Dems to choose between left and right, and may in due course force a split. If Nick Clegg is not skilful, his party will suffer its worst schism since the last times it entered coalition with the Tories in the national economic interest, in the 1920s and 1930s. Jostling for status, backbiting over defence, bitter disputes over spending cuts, Simon Hughes doing his thing: the CCC's offspring – "new politics" and the "Big Society" – will have a difficult birth.