What makes the ideal coalition?
As David Cameron and Nick Clegg marked their first 100 days of power sharing, I've been on the trail of a how-to guide to constructing the perfect coalition.
My first stop is Derby. The political parties have been bed-hopping here for years. One minute it's the Conservatives and Lib Democrats running the council together. Then Labour held the reins, bizarrely courtesy of a deal with the Tories.
According to Chris Williamson, the new local MP and a long-time councillor, Labour came to this arrangement through gritted teeth. "We didn't get into bed with the Conservatives. They were in the same room; not in the same bed."
They did so, he tells me, so as not to jeopardise various regeneration projects. And there was another reason: "It was a mutual loathing of the liberals."
So what's wrong with two parties working together, particularly in a city which often produces indecisive results at the ballot box? Matt Holmes, the Tories' deputy leader, was distinctly unenthusiastic. His party pledged at the May local elections not to do deals.
"We wanted to have our manifesto in full, implemented as much as we could without compromise; we made that pledge and stood by it." Red meat politics or bust. Except the numbers didn't add up. So they had to come to a loose arrangement that, officially, doesn't exist.
As for Cameron's love-in with Clegg, Mr Holmes notes drily: "What happens nationally doesn't have to happen locally."
So what about one level up? Devolution for Scotland and Wales was designed - by Labour - to produce a new kind of politics. The voting system almost presupposed a continuum of coalitions or other arrangements.
So has that experience also left the protagonists feeling jaundiced? Not in the slightest says the Lib Dem's Mike German, who did two terms as deputy first minister at the assembly in Cardiff.
He has some advice for those in power at Westminster, particularly for Mr Clegg: "It's absolutely the case that a junior partner in a government will need to make sure that they get the credit for things which are theirs in the coalition and for the credit which is jointly theirs within the government."
Jack McConnell served for six years as First Minister in Scotland, working with the Lib Dems - Labour's new enemy. He provides some tips for the new national coalition: have a clear cross-party agreement, a sense of purpose, a crisis-resolution process when things go wrong and a mechanism for ensuring that both sides' grassroots do not feel left out. But the most important ingredient, he says, is trust.
Mr McConnell then takes a swipe at those in Labour who have been incessantly attacking the Con-Lib alliance at Westminster: "There's a public willingness to go with politicians who are seen to want to compromise and to work together," he tells me.
"Labour needs to be very careful and not position ourselves as being the party that is operating out-with the national interest."
Ultimately, for all the talk of policies, programmes and structures, it surely comes down to people. What makes them come together and stick together? Who better to ask than the agony aunt, Virginia Ironside. She likens the coalition agreement to a marriage vow, or perhaps a pre-nup.
"What keeps partners together is the very decision to stick together, through thick and thin", she says. "Even though both spouses - or party leaders - might hate each other from time to time, they have made a commitment to stay together, and that's what will ultimately prevail."
Some practical guidance not just from Virginia Ironside, but from the others too, to messrs Cameron and Clegg as they attempt to keep their marriage on track. At least for five years, but then apparently, everything's up for grabs.
A perfect coalition? That's unattainable. But a stable and strong one might just work this time, and, who knows, at other times too.
John Kampfner presents Beyond Westminster, on BBC Radio 4 Saturday 21 August at 1100 BST