Recently the Conservative and Liberal Democrat History Groups formed, appropriately enough, a coalition.

Theirs, however, was a short-lived affair, contrived to mark the centenary of the Liberal-Conservative coalition government formed in May 1915.

It followed two military setbacks, one domestic and the other foreign: a "Shell Crisis" at home (there had been severe shortages) and, in Turkey, the disastrous Gallipoli campaign. To stave off a political crisis, H. H. Asquith (the Liberal MP for East Fife) invited senior Conservatives to join his Cabinet.

The most recent general election, the second of two held in 1910, had produced what would nowadays be called a "hung" or "balanced" Parliament, with the Liberals on 272 seats and the Conservatives with 271 (although the latter party got more votes). John Redmond's Irish Parliamentary Party, therefore, held the balance of power with 74 MPs.

Of Scotland's 70 seats the Liberals won 53, the Conservatives 10 (although they weren't far behind the Liberals in terms of votes) and Labour just three, all of which serves to illustrate how swiftly long-established parties can rise or fall: by the 1920s Labour had displaced the Liberals, while the Tories had become much stronger.

There are also contemporary parallels. Between 1910-15 the Liberals were sustained in power by Redmond's 74 MPs on the basis that Home Rule for Ireland would finally be delivered; a century later many envisage - with good reason - dozens of SNP MPs propping up a minority Labour government after the 7th of May.

History, however, only takes us so far, and a lot of Nationalists appear to have convinced themselves that inter-war politics offers some sort of guide as to what might happen this time round. It does not. Sure, minority parties ended up forming governments in 1918, 1924 and 1931, but the context in which they did so was so far removed from early 21st-century politics that it'd take more than a newspaper column to do it justice.

But as we hurtle towards what looks like one of the most important elections of the post-war era, it's not a Liberal-Tory coalition but a Tory-Lib Dem government that will submit itself to the country. Several polls suggest Labour and the Conservatives - like the Liberals and Tories in 1910 - are at level pegging in terms of likely votes and seats, thus speculation of another hung Parliament.

For various reasons - as I've argued in this column before - I think the smart money is still on a minority Conservative government. Indeed, speaking at a fringe meeting at the Scottish Tory conference late last week the MSP Murdo Fraser urged precisely that, arguing that while coalition with the Liberal Democrats had provided stability, in other respects it was holding the Tories back (on, for example, energy policy).

Minority government also remains the preferred outcome of the backbench 1922 Committee. Senior Tories, of course, maintain that they're confident of a majority - in Edinburgh last week Lynton Crosby, the so-called "Wizard of Oz" told conference delegates that just 11,500 votes could secure an additional 20 Tory MPs and thus an overall majority - but privately few consider this a realistic prospect.

As has now become obvious, the Liberal Democrats are heading for heavy losses - perhaps half their current tally of MPs - with an even worse result in Scotland, a decline much swifter that their "strange death" a century ago. At the same fringe event David Mundell, the Conservatives' only Scottish MP, revealed a wager with Craig Harrow, convenor of the Scottish Liberal Democrats, that there would, as a result of the election, be more Tory MPs in Scotland than Lib Dems.

That isn't impossible, although talk of a Scottish Conservative revival is, as ever, premature. The fact the election campaign in Scotland has ended up being cast as a Labour-SNP battle doesn't help, for it encourages tactical voting. Anecdotally, I've encountered many Tory voters who have resigned themselves to voting Labour to "keep the SNP out", a phenomenon of which party strategists are acutely aware.

The post-referendum dynamic also works against Unionist parties like the Conservatives, for while the No vote is numerically stronger than Yes it is also split three ways. Realpolitik would dictate that the Tories, Lib Dems and Labour should merge into a catch all pro-Union party in order to take on "the 45" (many Nationalists, of course, believe that already to be true).

In retrospect, the Liberal Democrats squandered an historic opportunity to exert real influence following the last election. As David Mundell admitted last Friday, he remained mystified as to why Nick Clegg hadn't made tuition fees his red line rather than electoral reform, and also his failure to insist on a proper departmental brief rather than the non-job of Deputy Prime Minister.

The first two Scottish Executives (1999-2007) clearly demonstrated that a minority party could extract real concessions and remain electorally popular. This time round, however, it has proved disastrous. It brings to mind a Second World War analogy: although occupied countries hated the Nazis for invading them, they reserved particular loathing for those who collaborated in order to make it possible.

I'm not, of course, suggesting modern Conservatives are analogous to the Nazis (although other critics, I suspect, wouldn't be as reticent), but the Liberal Democrats will find guilt by association impossible to escape, something which in itself also makes a second Tory-Lib Dem coalition extremely unlikely, even if the numbers added up.

Who forms the next UK government, however, is but a transient concern in the broader context of the ever-changing British constitution. If, as seems likely, the Lib Dems all but disappear in Scotland while Labour retreats southwards and the Conservatives fail to recover, then the pressures on the constitutional status quo will only increase.

The Union of old, that which appeared relatively stable even amid different constitutional crises more than a century ago, increasingly looks like a spent force. At the Scottish Conservative conference Murdo Fraser chastised the Liberal Democrats for having been "useless" proponents of federalism, his implication being that his party should take up the mantle.

Only federalism stands any chance of sustaining the UK, and given the Conservative Party exists - at least in part - with that aim in mind, it would do well to reflect more deeply on the long-term consequences should it form a minority or majority administration in a few months' time. The assumption in some quarters that things will soon "get back to normal" (i.e. a Conservative-Labour duopoly) is almost laughably complacent.

The Fixed-Term Parliaments Act makes the prospect of two general elections in one year (as was the case in 1910) remote but not impossible. If no administration is formed within two weeks of polling day or, even if it is, two thirds of MPs desire dissolution, then five-year terms become academic. One would hope there's little appetite for history to repeat itself, as Karl Marx famously put it, "the first time as tragedy, the second time as farce".

DAVID TORRANCE