Nicola Sturgeon presents her wish list to Labour

In politics, there are two sorts of election manifesto. There is the wish list written by a party that has no realistic chance of winning power and does not expect to implement any of the contents. And there is the sort setting out a genuine prospectus for government.

Traditionally, the Scottish National party’s manifesto fell firmly into the first category. Indeed it was something of a thin wish list as the separatist party claimed to want little from Westminster. But at this year’s general election it aspires to the latter, buoyed by the astonishing surge in support the SNP is enjoying north of the border.

With just over two weeks to go before the vote, opinion polls have the party on course to win most of the 59 seats in Scotland — the only ones it contests. As the two main UK parties are running neck and neck, such a result could conceivably leave it holding the balance of power in the next parliament.

Should this happen, the SNP leader Nicola Sturgeon has already promised to keep the Conservatives out and prop up a minority Labour government — albeit on an issue-by-issue basis and taking no responsibility for its actions. To the extent its manifesto is therefore a wish list, it is one the SNP would seek to foist on Ed Miliband and his party should Labour take office after May 7.

Looked at from a position of cold political self interest, focusing on Westminster makes eminent sense for Ms Sturgeon. Since last September’s referendum, the fall in oil prices has further undermined the case for separatism. Independence, or even the full fiscal autonomy the SNP claims to favour as a halfway house, would leave Edinburgh with a deep black hole to fill. Far from ending austerity, as Ms Sturgeon glibly promises, she would be introducing a Caledonian version of her own.

Deploying an SNP bloc in the UK parliament to extract concessions offers a more promising result. Either these are delivered by Labour, in which case the SNP takes credit, or they are not, in which case the argument for independence is given a further push.

The tactic, of course, requires a new vocabulary. Gone are references to independence, a word that appears only once in the text. Instead Ms Sturgeon talks about extending the “hand of friendship” to England, Wales and Northern Ireland and building a “progressive alliance” across the whole UK.

What this means in practice is a bit of a mish-mash. Parts of the manifesto are pitched slightly to Labour’s left: for instance, the SNP would slow the pace of fiscal consolidation and hand more cash to the National Health Service. Some bits are unobjectionable, such as devolving more power to the north of England. There are a few nationalist shibboleths, such as the commitment to nuclear-free defence, which are apparently there to cheer the faithful.

But it is on the constitutional questions that the unseen small print abounds. The SNP would push for a maximalist interpretation of the Smith Commission, set up to amend the devolution settlement after the referendum. Ms Sturgeon’s aim would presumably be to extend Edinburgh’s economic powers while preserving the financial support Scotland receives from the UK. Trading taxpayers’ cash for Scottish votes would imperil not just Labour, but the union’s future.

Ms Sturgeon is not, as some have termed her, the most dangerous woman in Britain, nor is it illegitimate for her party’s MPs to maximise their influence in the Westminster parliament. Her manifesto, however, contains unseen pitfalls for Mr Miliband and the country as a whole should he seek to implement it to secure entry into Downing Street. This is one wish list he should firmly resist.