Sam Ghibaldan: Why a Labour deal with Clegg would make sense

So what's going on? Well, there can be little doubt that part of the Lib Dem strategy is to place pressure on the Tories. The message is clear: agree to a referendum on proportional representation, or there's no deal.

In an odd way, this might strengthen David Cameron's hand as he seeks to drag the Tory party towards compromise. The Tory leader is in a bind, laid bare by his remarks on Friday afternoon. In a statesmanlike and carefully constructed speech, he wriggled between the need to buy Lib Dem support and reassuring his party that he expected to see the Tory manifesto become the basis for government policy.

Four days down the track, Cameron is having difficulty persuading his party that, with no mandate to govern, they can't expect to get everything their own way. They need to get real. The electoral facts speak for themselves: across the UK nearly two-thirds of voters opposed a Tory government; even in England over 60 per cent voted for other parties.

But the Liberal Democrat decision to enter talks with Labour is about more than placing pressure on the Tories. Though Clegg's party would be prepared to reach agreement with the Tories in the national interest, they would do so reluctantly. One of the few things both parties share is mutual antipathy. Though there are significant differences between them, many Liberal Democrats feel marginally closer to Labour.

Since Thursday night, we have heard one phrase repeatedly – the national interest. But what does that mean? Certainly, it means a stable government. But for a government, working in the national interest means the policies you pursue must address the priority issues facing the country.

There can be little doubt that the issues that dominated the election campaign were safeguarding the economic recovery and political reform. The Tories stood isolated on their policies in these areas. There was far more in common between the positions of the Liberal Democrats and Labour. And, crucially, the majority of voters backed them.

But when it comes down to it, what counts is the number of votes a government can rely on in the House of Commons. The arithmetic is interesting. In the new House of Commons, 314 MPs (306 Tory and eight DUP) campaigned for immediate public sector funding cuts and in opposition to electoral reform. In contrast, 319 (258 Labour, 57 Liberal Democrat and four from Northern Ireland parties aligned with them – the SDLP and the Alliance Party) campaigned to maintain public spending for the present to allow the economic recovery to stabilise, and to reform the electoral system. Add to this the Scottish and Welsh nationalists – and even the solitary Green – and the figure rises to 329.

So, a Liberal Democrat and Labour government could offer stability. However much the Tories bluster, it would be a government composed of parties that between them had won a majority of votes.

Of course, any attempt to secure some agreement between the Liberal Democrats and Labour would face significant obstacles. As I write, it seems that the Tories are preparing to offer the Liberal Democrats a referendum on the Alternative Vote system. It is not favoured by the Liberal Democrats, as it doesn't fairly reflect people's votes, but it is arguably an improvement on first past the post. It is also Labour's current policy.

How is this all going to turn out? It does seem clear that Tory claims the public wouldn't forgive the Lib Dems for reaching an agreement with Labour have rightly failed to pressurise Clegg's party. Anyone who'd like to see Cameron as prime minister almost certainly voted Tory last Thursday. The significant majority who didn't are probably reluctant to see Cameron handed the keys to No. 10. The Lib Dems are no more likely to suffer electorally from a decision to work with Labour than with the Tories.

Sam Ghibaldan was a special adviser to former Lib Dem deputy first minister Jim Wallace.