Why do the Conservatives this morning issue a poster showing a mini-Miliband popping out the pocket of Alex Salmond? Not because it's funny, but because they know it works.
Focus group work in the England tell Tory strategists that voters fear the idea of the SNP having influence on a Westminster government. That worry makes them less likely to vote Labour.
Labour is now caught in a classic pincer movement by the SNP and the Conservatives, as the polling arithmetic shows that Labour falling short of a majority without SNP votes.
Cameron cannot advance the Tory cause in Scotland but he can try cutting the legs from under Labour in England, where the two main parties are tied.
If he raises the fear of a Labour-SNP coalition it turns voters off Labour in these English marginals. That could just be the difference between the Tories being able to form a coalition or the end of Cameron's career.
Alex Salmond tries to be as helpful as he can, claiming at his Gordon constituency adoption meeting on Friday that Westminster will dance to a Scottish tune. (He must be getting tired of saying that every time he stands for Westminster).
This time he added the rebalancing of infrastructure funding away from London to the list of SNP demands. A populist enough message north of Watford, but a very different signal to the London media who pick up the cue to warn their listeners and readers of the dangers of nationalism.
Why does Salmond say that? Because, for different reasons, both he and David Cameron want the same result -a Tory government.
So while Jim Murphy and Labour MPs say they are rebuilding their Scottish constituency defences brick by brick against the SNP surge Cameron is eating away at the foundations of a Labour government by stirring nationalist fears in the south.
For the Tories nationalism is a handy tool indeed and Cameron appears willing to encourage a nationalist surge with out caring for the consequences. A Tory government would not be seen as having legitimacy in Scotland with just one MP and the cuts to come will cause even more pain.
Add in a Tory referendum on the EU causing perhaps a constitutional crisis as well as one of democratic legitimacy and the ground is laid for another Scottish independence referendum.
The timing would be of Nicola Strugeon's choosing as it is not reckoned the SNP manifesto for 2015 or 2016 will bind the leadership to a vote within a specific timeframe.
Is the old telephone number for Scotland Yard and just about the right handle for the Westminster Editor of the Scottish Daily Record. I mostly patrol Westminster but this is my personal blog, taking in everything from my native Isle of Lewis to the Isle of Dogs in London. You can read my journalism at www.dailyrecord.co.uk and you can contact me directly on torcuil@gmail dot com