One of the great things about being the parent of an almost nine year old is that you get to read (or re-read) children's classics along with them rather than to them. My daughter is reading the Harry Potter series for the first time, and I'm re-reading them in turn after she finishes each volume, so we have something to talk about. She's reading the last one just now, so I've been reading the sixth, Harry Potter and the Half-Blood Prince. Which contains an interesting commentary on current political events...
Early in the book, the evil sisters Narcissa Malfoy and Bellatrix Lestrange (say what you like about Rowling's ability to write dialogue, but she has a great way with names) visit Severus Snape to enlist his help in assist the former's son, Draco Malfoy, in the task that Voldemort has set him. (We later find out that this is to kill Professor Dumbledore.) Snape swears a mighty vow, magically sealed to be an Unbreakable Vow, and with Bellatrix as the 'Binder' (magical guarantor) that he will protect Draco and if needed carry out the deed himself. I've not seen the movie from this book but clips are available of the vow-casting online - they make for a chilling scene.
The point about an unbreakable vow is that it's (doh) unbreakable. If you break it, you die. It's a big undertaking. Not to be taken lightly. Not to be used as a bargaining chip in an argument you're afraid you might be losing.
And so to politics. A vow was solemnly made this week by three political parties leaders, sealed not by a magical spell but by their own reputations, and guaranteed not by a wizard but by a former Prime Minister of the UK. But they did promise faithfully that "all three main parties will deliver change for Scotland".
Such a vow is not unbreakable in quite the same way as Snape's vow. Cameron, Miliband and Clegg will not die if they renege on this vow but their reputations will be in tatters if they do. Moreover, the whole basis on which they finally turned around the referendum, persuaded the Scottish people that voting No wasn't just a resumption of the status quo, would be in tatters. Moreover, it would fuel the cynical belief across the whole UK that You Can't Trust Politicians. And fuelling that belief doesn't just threaten the Scotland-England relationship, it risks letting in the anti-politicians, the populists like Nigel Farage and worse ones further right than him, who currently are just a nuisance but given a measure of power could be extremely dangerous.
So in a way this vow is just as unbreakable as Snape's vow. Except that if they break this, what they risk destroying isn't just their own reputations - it's the future of the United Kingdom as a viable polity, and even of democracy itself within these isles.
The vow must be kept.