NIGHTMARE! Ed Miliband as PM, propped up by Alex Salmond ‘calling the tune’ if Labour gets into Downing Street pic.twitter.com/uNFHs5deTo

— Grant Shapps (@grantshapps) March 9, 2015

Why for Dave the strong Sturgeon performance was a sideshow

Earlier this campaign, the Conservatives unveiled the above poster showing Ed Miliband in Alex Salmond’s pocket; the inference being that in a hung parliament it would be the SNP pulling Labour’s strings.

Nicola Sturgeon’s very capable handling of Thursday’s debate did nothing to reduce the likelihood of a large SNP delegation holding the balance of power after May 7. What it may have done is change people’s opinions of how they’d view that event.

The first question is what underlines the assertion in the poster? Presumably the point is that the SNP would demand ever-greater powers and monies to be sent from England north of Hadrian’s Wall, as Farage put it (one assumes he was using shorthand and doesn’t actually believe they’d demand Northumberland too). The second is who is it aimed at and the third is will they still believe it?

The swing votes this parliament have never been between Con and Lab. The votes the Conservatives have lost since 2010 are predominantly to UKIP (two-thirds of them in the last Populus poll, for example, excluding don’t knows). But do UKIP voters see the SNP as a sufficient threat to their interests to switch to the Tories to block them?

The polling immediately after the debate gave Sturgeon reasonable scores among UKIP supporters. For example, according to ICM, 60% said she performed quite well or very well and with YouGov, UKIP voters scored her at 5.4 out of 10 – the same as David Cameron and behind only their own man. However, that cuts two ways. A capable opponent who stands for the opposite of what you is more of a threat than a poor one, especially if the perception is that the tail has a biddable dog to wag.

So is the thinking behind the poster still viable? I’m not convinced. Although the message is probably strengthened by Thursday’s debate – though Miliband did reasonably well himself – the main problem is the logic: it’s simply too tenuous a set of tactical connections for the great majority of swing voters to act as needed. Put another way, even if you agree with the poster, what are you supposed to do?

And yet the truth of it is real enough: a minority Labour government would be very likely to be reliant on the SNP, vote by vote and budget by budget, and would inevitably look for concessions – which, to be fair, is what they’re there for.

There is one other relevant dynamic. The YouGov poll this week putting the Tories on 37% was probably top-side simply on sampling fluctuation but nonetheless proves the Blues to be within striking distance of their 2010 total. To repeat their seats total, however, requires Labour to be back down where they were too. (As an aside, to have recorded 37% despite having lost so much support to UKIP is quite a remarkable achievement). In essence, assuming they can’t get a direct swing, the Tory campaign has to shave 6% off a combination of Labour’s pre-existing core vote and the Lib Dems they gained in 2010 – and it has to come in England and Wales as Labour’s Scots losses are already maxed out.

Which is why although Sturgeon’s performance matters (a poor one would have brought a lot of expected SNP gains back into play), it’s not as critical as those of Clegg, Bennett or – if he can make disproportionate inroads against Labour, Farage. And the first two did poorly and the latter scored more off Blue than Red. Miliband will be happy enough with that.

David Herdson