You might remember that a few weeks ago, the Labour party lied through their teeth in an attempt to scare people who were thinking of voting SNP - by claiming it was a "FACT" that in a hung parliament, the largest single party gets to form a government. When it was pointed out that there were historical precedents of the second-largest party forming a government (most recently when Ramsay MacDonald became Prime Minister after the 1923 election), they hurriedly changed their line to "for the last 90 years, the largest party has always formed the government". The implication was that this amounted to much the same thing, ie. something that hasn't happened for nine decades must be extraordinarily rare, and thus unlikely to happen now.
But here's the thing - there have been twenty-five general elections over the last century, and just four have resulted in a hung parliament. Those four occasions were 1923, 1929, 1974 and 2010. One of them resulted in the second-largest party forming the government. I don't know about you, but a 25% strike rate seems pretty decent to me. And it gets even better, because on at least two of the other three occasions, the second-largest party made a serious attempt to form a government. In February 1974, Edward Heath's Tories were narrowly beaten into second place, but immediately opened coalition talks with the Liberals, and offered the post of Home Secretary to Jeremy Thorpe. There were even suggestions that Heath might step down in favour of Willie Whitelaw to make the deal more palatable. And then of course there was 2010, when the Liberal Democrats agreed to Gordon Brown's request to open up formal coalition negotiations with the second-placed Labour party. Those negotiations were eventually scuppered by right-wing Labour politicians such as Tom Harris and David Blunkett, who toured the TV studios openly campaigning for David Cameron to become Prime Minister.
So what Labour should really be saying is : If we're the second-largest party in a hung parliament after May, history tells us there's 'only' a 75% chance that we'll make a serious attempt to take office, and if we fail it'll probably be because our own members sabotage us. But somehow that doesn't sound like a very compelling argument against voting SNP.