Craig Murray has asked for clarity on whether the SNP would withdraw support for a minority Labour government if it joined forces with the Tories in the Commons to force through the renewal of Trident. I think the SNP have been pretty clear, actually - the scrapping of Trident would be an absolute condition for a confidence-and-supply arrangement, and without it Labour would have to go it alone and seek support on a vote-by-vote basis. That would mean looking to right-wing parties like the Tories, UKIP and Lib Dems to get things through that the SNP would never support (such as Trident), and it would mean looking to the SNP, Plaid Cymru and the Greens to get things through that the Tories would never support (such as an increase in the top rate of tax).
But there has been a very strong indication that the SNP would not do anything to bring about an early election, which implies that Labour would not be 'punished' in a confidence vote for the renewal of Trident. And if you think about it, that's perfectly rational - an early election would have absolutely no prospect of producing an anti-Trident majority in parliament, so nothing would be gained by bringing a Labour government down. (And much might be lost, if the arithmetic after a new election was less favourable.)
That's not to say that the SNP are powerless to do anything about Trident in a hung parliament, though. As I've speculated before, Labour may quickly be worn down by trying to survive day-to-day on a vote-by-vote basis, and the security of the formal deal they originally shunned might start to look very attractive after a few months - particularly if the opinion polls were suggesting that they would lose a snap election. If the SNP's red lines for a deal hadn't shifted by then, Trident's days would be numbered.
Incidentally, I don't follow Duncan Hothersall on Twitter anymore (mainly because he seemed to block me for a while, which automatically deleted me from his followers' list), so I'd be curious to know what logical gymnastics he's been partaking in over the last few months to square his own views on Trident with continued support for Labour. During the referendum, he repeatedly told us he wasn't interested in simply shifting the location of Britain's nuclear weapons, but instead wanted to abolish them altogether. Well, we now have the SNP asking for a mandate to go to the UK parliament and abolish Trident altogether, while Labour are asking for a mandate to go to the UK parliament and spend billions of pounds renewing Trident.
Why is Duncan voting Labour? Does he even know?