I want to make a big, open and comprehensive offer to the Liberal Democrats,” said David Cameron on the afternoon of May 7, 2010, as he addressed the media following the inconclusive general election result of the night before.
Well, we know what happened next. After several days of intrigue in which Lib Dem leader Nick Clegg tried to play both ends off against the middle in the hope of extracting better terms from the Tories, the deal was finally done and the Coalition government was formed.
Despite some initial scepticism that it would last the course – not least from yours truly – it has proved remarkably durable and, aside from the occasional bust-up, remarkably stable.
But what if the Lib Dems had said no to Mr Cameron’s big, open and comprehensive offer? What would have happened then, and five years on, where might British politics be now as a result?
The first thing to say is that Mr Cameron would still have become Prime Minister. Although Gordon Brown squatted in Downing Street for several days attempting to patch together a deal with Mr Clegg, the numbers never really added up and there was significant opposition within Labour to such a pact.
So Mr Cameron would have led a minority government, perhaps initially with a ‘confidence and supply’ arrangement with the Lib Dems in which they agreed not to vote down the first Budget and Queen’s Speech, but with a general expectation that a second election would follow within a year.
Labour would still have elected a new leader to replace Mr Brown in the summer of 2010 – but in that changed situation the chances are it would not have been Ed Miliband.
With another general election in the offing soon, and the prospect of a swift return to power, Labour would almost certainly have elected the ‘oven-ready’ Prime Minister-in-waiting, the then South Shields MP David Miliband.
I could go on. Would the Tories have then cemented their grip on power, winning an outright majority in a spring 2011 poll having proved their economic competence and general fitness to govern over the preceeding months?
Or, more likely, would the elder Miliband brother have summarily ejected them from office against the backdrop of the double-dip recession induced by George Osborne’s 2010 ‘austerity’ Budget which choked off what had been a nascent recovery under Mr Brown?
Who might then have succeeded Mr Cameron as Tory leader? Not Boris Johnson – he was too busy organising London 2012 – but perhaps David Davis, the man who had previously been frozen out of the Tory Party’s inner councils and who would thus have been unsullied by the failed 2010 and 2011 campaigns.
Would we, in fact, now be approaching a ‘Battle of the Two Davids’ election with Prime Minister Miliband seeking a second term against the perennial poster-boy of the libertarian Tory right?
Well, we will never know. But entertaining as it is to indulge in political ‘what ifs,’ there is a sort of serious point to all this.
Because, despite having given us five years of unexpectedly stable government, the idea of coalition now appears to have fallen sharply out of favour with Britain’s political elite.
The ongoing fragmentation of British politics into a multi-party system, allied to the closeness of the two main parties in the opinion polls, means we are very likely to have another hung Parliament after May 7.
But this time round, it seems much less likely to result in a formal pact, and more likely to lead to the sort of scenario outlined above - a short-lived minority government, a second election, and at least one change of party leadership.
The big losers of the UK’s brief flirtation with coalition are of course the Liberal Democrats, who longed for such a taste of power only to see their support haemorrhaging across the country.
Ten years ago, it looked like they were set to become the main challengers to Labour in the North East. Now that mantle may well fall to a very different party – Nigel Farage’s Ukip.
Of course, Mr Clegg would argue that had they said no to Mr Cameron’s deal and remained a party of protest, they would have paid a similar electoral price - but we’ll never know the answer to that one either.
One thing is for sure, though. They’ll think twice the next time someone makes them an offer – however big, open and comprehensive it may be.