Looking at the parliamentary arithmetic (and after 13 years of governments who had big enough majorities to be able to pretty much ignore parliament, isn't it nice to be talking about the parliamentary arithmetic again?) Tories plus Lib Dems, with a combined total of 363 MPs, is by far the most stable coalition option available.
The problem is that there's not enough in it for the Lib Dems to make it a goer - unless Clegg is a fool, which I don't think he is.
I can see the attraction from DaveCam's point of view - he gets to govern on a slightly more moderate version of their programme (which will play well to swing voters). Dave will be able to face down the Tory hard right (of which more in a moment) by pointing out that circumstances are difficult and being in coalition demands a degree of moderation. He won't give way on electoral reform - he'll have a commission to discuss it and changes will be cosmetic if any.
After which point, he calls another election, wins an overall majority (if he can), and the Lib Dems are unceremoniously dumped - having achieved almost nothing.
What's in this for Nick Clegg? The offer of a few cabinet posts, implementing a slightly modified Tory programme. No PR. Some commentators have suggested that the electorate will reward the Lib Dems for their commitment to stable govt. Er.... they're much more likely to drop the Lib Dems like hot bricks for being Tory collaborators. Especially if Labour presents a more palatable option under a new leader next time round.
I think Clegg is just going through the motions here. I can't see a formal coalition between Lib Dems and Tories working out. He'd be signing his political death warrant.
What about the alternative coalition which parliamentary arithmetic allows (just about) - a Labour-Lib Dem - plus 4 or 5 minor parties "rainbow" or "traffic light" coalition? The numbers stack up as follows:
Labour 258 + Lib Dems 57 + SDLP 3 + Alliance 1 + Green 1 = 320. Just short of a working majority, but for this govt to go down, there would have to be 321 votes against them. The opposition would be: 306 Tories + 8 DUP = 314. If both the SNP and Plaid Cymru tagged on to the Tories and DUP, they could bring down this coalition. But that's unlikely to happen in my view. The coalition could offer them a better deal (however slightly) than they'd expect from a Tory govt, and then they're effectively onside.
Make no mistake - this would be a lashed-up, opportunistic coalition (so would a Tory/Lib Dem arrangement, but the numbers are a lot stronger for that one). It would demand almost total voting loyalty from Labour and Lib Dem MPs to work out - so the likes of Frank Field (to name an obvious loose-cannon maverick) would have to somehow be kept onside. One way of doing this (as practised by Jim Callaghan in the late 1970s, the last time the numbers were like this) would be to turn crucial parliamentary votes into confidence motions - so the govt falls if Labour MPs vote against a bill to introduce proportional representation (which would be one of the main objectives of the coalition). It's also highly vulnerable to by-election losses, particularly if there's a public backlash. The Tory press would do its damnedest to make sure this coalition was unpopular.
There's also the practical matter that I don't think Clegg particularly relishes the thought of working with Gordon Brown - but Brown won't want to quit just yet to give way to another Labour leader. Perhaps if he said he'd stand down just before another election after the necessary PR legislation has been introduced that would be just about acceptable to all sides. It's a big ask, though.
The questions of democratic legitimacy of this coalition, which are being asked by commentators on the right, are bollocks, as Will Hutton points out in the Observer. It's not a "coalition of the defeated" because if you count holding an overall majority as a measure of "winning" and not getting an overall majority as "losing", EVERY party "lost" the election - including the Tories - and anyone who can put together a govt that can't be voted down is in the "winners". In terms of public opinion, this coalition would represent around 55% of votes cast - 19% more than the Tories on their own - so it's actually much MORE legitimate than a minority Tory govt (which I'll come on to next).
But I still think there's a lot less than 50/50 chance that we'll get this. It would be an unstable and rickety arrangement. And if it does collapse before delivering voting reform, the consequences for the left - and the middle - of British politics would be disastrous.
The safer bet for Labour and the Lib Dems - in some ways - is to let Cameron form a minority govt. The Tories would be allowed to pass a finance bill and implement the less controversial aspects of their programme, but some stuff would be a no-go area - for example the Tories' voting reform bill, which aims to change constituency boundaries to more or less guarantee a permanent Conservative majority. That's their idea of voting reform - the system is rigged against them, so instead of a proper reform, they will re-rig it to suit themselves. One has to admire the chutzpah of this, but there's not way the other parties would let them get it through.
Which is a very good thing, because without it I think Cameron will find it difficult to win the next election. People make parallels with 1974 - when Harold Wilson's minority Labour govt secured a tiny shift of voter support in their favour to win a majority of 3 in the second election that year - but why should we believe Cameron will get a honeymoon that lasts any longer than (say) 3 months? The economic problems seem to be getting worse, not better, in the short run, and the Tory spending cuts (which I would recommend Labour and the Lib Dems let the Tories implement just to show how crazy this policy is from an economic point of view) will provoke a 'double-dip' recession. Cameron will be under vicious pressure from the right-wing of his party to run a radical far-right govt, and given that his parliamentary position is so precarious, he'll find it difficult to resist the call of the nutters.
Meanwhile, the opposition parties can bring the govt down at the moment of maximum unpopularity, and - even if cash-strapped - Labour would probably win an election - or at least emerge as the largest single party - with a new leader under existing constituency boundaries in first-past-the-post. And then it's bye-bye Dave.
There is a huge argument raging on the blogosphere about whether Labour should go for the rainbow coalition or let DaveCam form a minority govt - assuming that the Lib-Con coalition talks fail. The best article I've found so far arguing for the rainbow coalition is Steve Richards in the Independent. As for supporters of letting Dave go it alone, Lance Price in the Guardian, and Richard Murphy on his blog, provide the strongest arguments.
On balance, I think Tory minority govt is safer. It gives Labour time - under a new leader, who should be elected ASAP - to work out a combined approach to electoral reform with the Lib Dems (and maybe other smaller parties as well) and synchronise their manifestos on this issue at the next election. Cameron of course has the power to call an election but so do they (by voting him down in conjunction with any combination of a few smaller parties), so it becomes a question of what the opinion polls are showing and who jumps first. The theme of the election next time may well be old politics (Cameron, leading a Tory party riven by infighting which has ALREADY BEGUN - only 48 hours after the results came out!) vs new politics (represented by a unified offer of voting reform from all serious opposition parties.
It's going to be just wonderful. Looking forward to it.