PM Cam's Scottish trip could be crucial

Come in Mr Cameron, you're cleared for landing

Idle speculation, the kind that fills the media vacuum before the TV debates, in today's FT about a minority Tory government seeking the support of nationalists to govern.

The scenario is that the Tories could be 20 or so seats short of a majority - not shown in the polls right now but the swing in marginals might be greater so they may get there. Three could, mights and mays in that last sentence but bear with me.

Instead of going to the hated Lib Dems and having to concede to demands electoral reform the Tories could turn to the Celtic fringes. The Democratic Unionists in Northern Ireland would provide nine votes and Lady Hermon, the independent formerly UUP MP will make it ten.

In Scotland the SNP might have seven MPs on current projections and Plaid Cymru three. That's another ten votes in the bag.

The SNP would get concessions and the list of demands, like releasing the fossil fuel fund isn't very ambitious, so Cameron could stay Union Jack blue and

The SNP say they wouldn't enter any formal deal - but nothing is for nothing. They would be handcuffed to a Tory Queen's Speech and to supporting a Tory budget.

I see Kirsty Wark nailed Salmond on Newsnight over voting on English issues, which the SNP do not generally do unless they see a chance of beating the government.

Salmond conceded that the SNP would "have to review our general attitude" to voting in Westminster. Mmm, that's an interesting hint which could make Cameron's promised visit to Scotland in the first week of a Tory premiership a real talking point.

The electoral cost for the SNP in propping up a Tory government can't be quantified, but it can be guessed at. Within a year the SNP government will face a Holyrood election and with the public sector being squeezed badly by that time they may reap a whirlwind.

Conventional thinking is that the SNP would welcome a Tory win because they believe it would strengthen Scottish support for independence. But supporting a minority Tory government would have consequences in Scotland. Be careful what you wish for.