UK Election 2015: SNP takes high road to Westminster
If the opinion polls are to be believed, the Scottish National Party (SNP), whose long-term goal is an independent Scotland, could be on the verge of a major breakthrough in the UK general election on 7 May.
An SNP breakthrough in Westminster would come just eight months after it was defeated in the Scottish independence referendum - when Scots voted "no" to leaving the UK. So how did it happen and what does it mean for the next British government?
The SNP has run the devolved government in Edinburgh on its own since the Scottish parliamentary election in 2011 and longer still as a minority administration, but now it looks poised to win a majority of the 59 MPs that Scotland sends to the UK parliament, making it a major force in Westminster.
The referendum in September led to a surge in Scottish political engagement.
The main Westminster parties - Labour, Conservatives and the Liberal Democrats - stood united against independence, a stance which appears to have irritated many of Labour's core voters who - if the polling proves correct - have warmed to the SNP's left of centre, anti-austerity message.
As a result, Labour faces being wiped out in Scotland.
The SNP's then-leader Alex Salmond stepped down after the referendum loss, but his long-serving deputy, Nicola Sturgeon, has capitalised on the party's surge in support to become the star of the general election campaign, on both sides of the border.
And the party continues to grow: the SNP is now the third largest party in the UK by membership, despite drawing support from a tiny population.
So what happens next?
The opinion polls suggest that a hung parliament - where no party wins a majority of seats - is the most likely outcome.
Ms Sturgeon has repeatedly offered to form a coalition with Labour, but Labour leader Ed Miliband has repeatedly ruled it out.
He has also ruled out a looser "confidence and supply" deal, under which the SNP would agree to support a minority Labour government on key votes.
It is a calculated strategy, but in ruling out a deal with the elected representatives of the Scottish people - assuming there is a large block of pro-independence MPs - Labour could alienate voters in Scotland still further and further increase tension within the union.
Ms Sturgeon has said Mr Miliband's refusal to work with the SNP could be the "last nail in the coffin of Scottish Labour".
But Mr Miliband knows his refusal plays well in England, where he is most likely to win the votes he needs.
How influential could the SNP be?
Without a coalition or deal, a possible minority Labour government would have to fight vote by vote, day by day, to get its programme through parliament, relying on the SNP to support them - and there are several potential political flashpoints.
Labour is committed to renewing the Trident submarines which carry the UK's nuclear missiles, at a cost of at least $36bn (£24m). The SNP is vehemently opposed to renewing Trident.
The SNP wants an end to austerity while Labour is committed to tackling the deficit, albeit more slowly than the Conservatives.
But, as Ed Miliband is well aware, the SNP has said it will never support a Conservative government.
He will be betting on them being compelled to support a Labour minority government rather than help the Tories back into power.
So the post-election future looks very hard to predict.
A re-run of the referendum is unlikely in the short term, but make no mistake: if the SNP wins anything like the number of seats at Westminster it is predicted to, it will have shaken British politics to the core.