Through an election campaign you either build a cage for your victory or a springboard. Given its strengthening lead in the polls, what is Labour building in terms of its relationships with the SNP in particular?

Lets take as axiomatic that Labour can’t govern for five years as a minority government. Rumours abound that Labour is toying with a wild game of brinkmanship whereby they present their budget to the House and dare the SNP to vote it down and be seen to let the Tories in. Such a move would be so transparently Machiavellian and contribute so needlessly to political turmoil that’s it’s a non-starter.

Labour has already ruled out a coalition with the SNP, which was never politically feasible nor desirable. So that leaves some kind of looser arrangement, like confidence and supply, which Labour sensibly hasnt ruled out. But while some kind of deal looks inevitable, Labour’s approach is muddled. Are they building a cage or a springboard?

In the leaders debate Miliband’s punches were aimed only at Cameron. But the French Memo was too tempting a target to ignore – jumping on the Tory/Telegraph bandwagon Labour spread the slur that the SNP really wants a Tory government to hasten a new and more winnable independence referendum. But is this the case? Are the SNP a fast track to Tory domination and the break up of the union or something much more positive instead?

There is nothing the SNP can do to create a Tory government. If they did they would be political toast. And they could not have been clearer about their intention to vote any attempt at a Tory government down.

That is because the SNP are now clearly to the left of Labour. They are anti-austerity and anti-Trident, have dropped the corporation tax race to the bottom and stand for mildly social democratic public services. They say things common sense things like ‘we should have time to retire before we die’ which stand out but shouldn’t.

Like all parties, and especially Labour, the SNP is complex, contradictory and far from perfect. But the trends seem clear – the SNP want what Labour people want. Sturgeon is a utilitarian nationalist, she backs independence as a cool rational act of a modern social democrat. In December 2012 she said this in an important and overlooked speech:

For me the fact of nationhood or Scottish identity is not the motive force for independence. Nor do I believe that independence, however desirable, is essential for the preservation of our distinctive Scottish identity. And I don't agree at all that feeling British – with all of the shared social, family and cultural heritage that makes up such an identity – is in any way inconsistent with a pragmatic, utilitarian support for political independence. My conviction that Scotland should be independent stems from the principles, not of identity or nationality, but of democracy and social justice.”

She went on, and it’s worth quoting at length:

Labour's argument is that Scotland should bear the storms of UK membership when the Tories are in office because, in the event of a Labour government, things will improve more than they ever could with independence. To me, that argument is deeply flawed. First, I simply do not believe that Scotland should have to put up with long periods of UK government led by a party we did not vote for. It is - surely - democratically indefensible that although the Tories have never won a majority of votes or seats in Scotland in my entire lifetime – or even come anywhere close – they have nevertheless governed Scotland for more than half of my lifetime. Second, it is clear from its record that for Labour to be elected across the UK, it must become something different to what Scotland wants. Social justice becomes a policy to be bartered against other interests - wars, nuclear weapons and welfare cuts. In the end the Blair government elected in 1997 was not an alternative to Conservatism. It was business as usual.”

Nicola Sturgeon and the rise of the modern SNP are a product of Labour’s failure to sufficiently promote social justice or democracy. What she and the SNP are showing is that more radical and daring politics chime with people.

So what we potentially have is a reordering of the anti Tory block – but the likely re-adjustment of seats from Labour to the SNP could make more radical politics more likely.

Now if you’re a dyed-in-the-wool Labour tribalist – this offends. Equally, if you are a to-your-finger-tips Blairite, convinced that Britain will never vote for anything more radical than the mild humanization of free market capitalism – then its equally offensive. But if all you want is to make Britain a normal place to live in again – then what’s not to like?

No one is saying Labour shouldn’t fight for every seat in Scotland – but its how they fight – burning every bridge in a scorched earth politics or leaving the way open to make a progressive alliance possible?

And there could be an electoral bonus from this approach. It’s going to matter hugely how Greens, the unaligned left and left wing Liberal Democrats vote in England where the principle enemy is the Tories. Labour could be making it clear to them, that while they fight for every seat, they would welcome a loose arrangement with whoever wants broadly what they want for our nation.

In the long run Labour can only save the Union and itself in Scotland by being more social democratic than the SNP. What would the utilitarian Nicola Sturgeon do then? The days of big single party majorities look to be over. One more heave won’t bring them back. The future will be negotiated. The question is with who and how? How Labour fights will shape whether and how Labour governs.