There is so little between two parties that have hated each other for so long

First, the SNP is on course to overturn decades of Labour dominance. The only time that the SNP reached more than 10 seats was in October 1974. Even after they became the biggest party in the Scottish Parliament in 2007, they secured only six (20 per cent) MPs in 2010. Now, we expect the SNP to follow up its landslide Scottish Parliament victory in 2011 with a large majority of Scottish seats next month.

Secondly, this will happen even though the SNP lost the referendum on Scottish independence and are not pushing for another one. For the casual observer, it will be difficult to work out why the SNP's membership surged after the referendum and why this has not reinforced the SNP's determination to try again promptly.

Thirdly, the SNP are pursuing a non-trivial relationship with a UK Labour party of government. For observers of Scottish politics, this is almost like a Labour-Conservative agreement in the UK. Even though Scottish devolution in 1999 came with the promise of new, less partisan, politics, the SNP-Labour relationship has seemed just as bitter and adversarial as anything Westminster can offer.

Yet, here we are talking about the SNP reigning in their constitutional ambitions to play a part in UK politics for the foreseeable future. Although their opponents describe them as a single-issue party, they have become just as adept at winning elections first and pursuing their policies second. They won't push for a referendum or further devolution at all costs. Rather, they are looking for a way to balance their long-term aims with a way to make their policies relevant to every possible election. This year, this means occupying ground to the left of UK Labour while doing what most parties have done in Scottish politics for decades: opposing "the Tories".

The SNP's manifesto reflects this shift. In almost all respects, the demands are tailor-made to an agreement with Labour. The manifesto makes the same noises about protecting Scotland's budget, implementing the Smith proposals and going a little bit further on constitutional change. Their policy aims, to protect state pensions, abolish the "bedroom tax", increase the minimum wage, boost NHS spending, reduce tuition fees in England, abolish the House of Lords, not hold an EU referendum and increase the representation of women in public life are almost identical to Labour's. The SNP have published what amounts to a list of Labour policies that they are happy to vote for: the reintroduction of the 50 pence top tax rate; a tax on bankers' bonuses; a bank levy; a mansion tax; a crackdown on tax avoidance; the abolition of "non-dom" status and reversal of the married couple's tax allowance.

This leaves only two "red-line" issues that aren't as clear cut as the parties suggest. First, the SNP want to abolish Trident and Labour describe a "'minimum, credible, independent nuclear capability"' but not renewal. Much depends on Labour's ability to put the issue off, to reflect the fact that many of their MPs would rather not renew. Secondly, the SNP are talking about fiscal autonomy in the long term, highlighting how long it has taken to deliver far less ambitious further-devolution plans so far and saying that they are prepared to see autonomy delivered over more than one parliamentary term. They have erased the most important red line. Overall, take away the SNP's call for independence and you see just how little there is between the parties that have hated each other in public for so long. What a remarkable turn of events.

Paul Cairney gave the University of Glasgow Stevenson Trust lecture: "Why does the independence referendum matter for the UK General Election?" The next Stevenson lecture will be given by John Curtice: "So Can Anyone Win? The Prospects for May 7 and Beyond." April 28 at 6 pm. stevesnsontrust@glasgow.ac.uk