Perhaps inevitably, there are signs of strain already. Lib Dem MPs Bob Russell and Mike Hancock received a warm welcome in the Labour lobbies when they rebelled over the VAT rise, as did those who opposed the academies bill this week.

Yet these rebellions are really just the calm before the storm. Disgruntlement over VAT was to be expected – the Lib Dems campaigned specifically against the tax rise they have just put through, and had to listen to their own campaign literature being repeated back to them in the Commons before the vote. The real tests, however, of the coalition’s fortitude won’t come until next year.

May 2011 could be crucial. Colleagues in the press tell me that if you conduct a poll on the favourability of the coalition as a whole, the response is quite positive. The term ‘coalition’ carries warm connotations of working together, playing for the team, and putting past differences to one side for the good of the country. However, if you poll the popularity of the constituent parts of the coalition, it’s not so good, and, for the Lib Dems, it is actually quite bad. Many people believe they have sold their souls for a few seats in government. Probably because it’s true.

For most parties in their position this would be difficult. But for the Lib Dems, a party built on its local government base but with no experience of the sort of collateral damage national incumbency can do, it’s downright awful. When they start to lose vast numbers of local councillors, possibly through defections as well as defeats, the pressure on Nick Clegg will be substantial.

In addition, May 2011 may well see the referendum on AV. I’ve always been an electoral reformer, and I see AV as an improvement on first past the post, but it hardly fills me with giddy excitement. In particular, it doesn’t achieve greater proportionality, and it can still exaggerate modest leads in the share of the vote into enormous parliamentary majorities. From conversations in the tearoom, I’m not the only reformer who feels this way. This lack of enthusiasm amongst genuine advocates of reform, plus the entrenched opposition of nearly every part of the Conservative party, will make victory in a referendum difficult.

If a referendum is held and then lost, the Lib Dem tribe will start to seriously consider what they are getting out of the coalition deal. Without major wins on their policy agenda, their role as a figleaf for the austerity drive looks desperate. Their role in some of the debates during the finance bill has been embarrassing. Danny Alexander is struggling badly in the Commons and looks far less assured than his Conservative deputy, David Gauke. But both Vince Cable and Chris Huhne are believed to have turned the role of chief secretary down, such is the poisoned chalice it represents.

Which brings me to my answer – either one year or five years. If the coalition can get through its first year and the AV referendum, I think it will hold together until the end. If it doesn’t, we’ll have a minority Conservative government and a general election soon after. My betting is that it will actually go the distance, though what sort of the state the Lib Dems (and indeed the country) will be in by then it anyone’s guess.