Reality Check: Another Scottish independence vote?
A Scottish independence referendum is not for First Minister Nicola Sturgeon to hold whenever she likes.
The constitution is a matter "reserved" to Westminster, so as with the referendum last year the Scottish government would need the UK Parliament's approval to hold one.
However, unlike last time, the UK government might not feel bound to allow a vote.
Parliament in London might say that the matter was recently settled and that it would not allow a series of votes in a "neverendum".
Senior SNP figures have said that the vote last September was a "once-in-a-generation" opportunity.
That said, if the SNP put the promise of a referendum in its manifesto and again got a majority for it in the 2016 Scottish Parliament elections, it could be difficult for Westminster to say no.
It would do the Union no good if the UK Parliament could be accused of trying to frustrate Scottish desires.
Election 2015 - Reality Check
What's the truth behind the politicians' claims on the campaign trail? Our experts investigate the facts, and wider stories, behind the soundbites.