There's been a unnecessary degree of confusion in recent months over the differences between coalition, confidence-and-supply, and a vote-by-vote arrangement. Much of the problem is caused by "creative fuzziness" in the language used by the political parties - for example, it helps the Tories in their aim of whipping up haggis-phobia if they pretend that there is no real distinction between a full Labour/SNP coalition and a looser deal. But I get the impression that a fair chunk of the media has been genuinely lost at sea on this topic all along.
One crucial point that needs to be borne in mind is that it's not necessarily an either/or choice - it's perfectly possible that this election could eventually result in spells of both confidence-and-supply and vote-by-vote. There's a relatively recent precedent for that. The parliament that was dissolved in the spring of 1979 after Callaghan lost a confidence vote had been elected way back in October 1974, but that election ultimately produced no fewer than four distinct types of government - firstly a Labour government with a tiny majority, then a relatively secure Labour minority government that was able to operate on a vote-by-vote basis without its existence being seriously threatened, then a formal confidence-and-supply deal with the Liberals, and finally a return to vote-by-vote, but by now with the administration under constant threat of being brought down. (It's too often forgotten that the Liberals eventually joined the Conservatives, the SNP and the Ulster Unionists in defeating Callaghan by a single vote - which according to Murphy-logic presumably means that Willie Rennie must be held personally responsible for Thatcherism.)
What we might see this time is Labour refusing to do a formal deal to begin with, but then quickly finding themselves worn down by the guerilla tactics that Alex Salmond and others have been hinting at. You could imagine that such a weak government might end up trailing badly in the opinion polls, so a snap election wouldn't be a realistic escape strategy, even if the problem of the Fixed Term Parliaments Act could be circumvented. A confidence-and-supply deal with the SNP might start to look like Miliband's least worst option, because at least it would guarantee him the passage of certain key parts of his programme, and give him some kind of track record to take to the electorate in 2020. In my view it would also suit the SNP, because a comprehensive deal on Home Rule is surely easier to attain via confidence-and-supply than vote-by-vote. I must admit I've been slightly puzzled by the apparent preference of both Alex Salmond and Nicola Sturgeon for vote-by-vote, although it may be significant that they've always stressed that confidence-and-supply is nevertheless very much "possible".
But what if the arithmetic doesn't fall in the SNP's favour, and the Tories are close enough to a majority that it's the Lib Dems, UKIP and the DUP that effectively hold the balance? I think there's still a big opportunity there, which doesn't rely on the SNP directly pulling the strings. If the Lib Dems refuse to do a formal deal this time around, a minority Tory government could end up losing an uncomfortable number of votes. Cameron might find himself becoming tempted by the idea of instantly transforming his administration into a majority government on English domestic matters, by putting forward a plan for genuine Scottish Home Rule tied to English Votes for English Laws. It's inconceivable that legislation to that effect wouldn't pass if both the Tories and the SNP voted for it. And there would be absolutely no bar to the SNP voting for it, because it wouldn't be an issue of confidence in the Tory government.
Another possibility is the one we were constantly talking about a few months ago - the "sweet spot for UKIP" scenario, whereby the arithmetic works out perfectly for Nigel Farage, and even with a relatively small number of seats he has enough leverage to force an EU referendum this year, without any prior renegotiation of Britain's terms of membership. If the UK voted to leave the EU, a quick independence referendum would be back on the agenda with a bang. However, that scenario is looking increasingly improbable - partly because UKIP's hopes of even a modest electoral breakthrough are gradually receding, and partly because opposition to EU membership seems to be dropping. But you just never know what twists and turns are around the corner.
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I had a Labour canvasser at the door on Tuesday for the first time ever in a Westminster campaign - which tells you something important in itself. I must admit I failed to practice what I preach by posing as an undecided voter and engaging him in a pointless ten minute conversation, but in my defence I did manage to hold his stare enigmatically for at least three seconds before telling him I was planning to vote SNP. He made no effort at all to dissuade me, and he didn't even bother asking for my reasons - presumably every last drop of nervous energy must be kept in reserve for the people who might still be won back.
He was a nice enough guy, although the all-red outfit seemed a bit "angry" to me, somehow.