Vote SNP, get Ed. Or David. Or...?

Parties have clashed over the consequence of voting for the SNP in the UK election Photo: Rui Vieira/PA Wire

Vote SNP and you'll get a left-wing Labour UK government under Ed Miliband.

Vote SNP and you'll get a right-wing Tory UK government under David Cameron.

That's the claim and counter-claim in Scotland ahead of the general election.

No surprise but the first comes from the Tories, the second from Labour.

In his speech to the Scottish Conservatives this afternoon in Edinburgh, David Cameron was ramming home his party's Caledonian narrative.

Prime Minister David Cameron speaking at the Scottish Conservative Party conference Credit: Danny Lawson/PA Wire

As the Prime Minister put it: "...if you thought the ultimate nightmare scenario was a Labour government, try this: Labour and the SNP in government."

Does Mr Cameron have any basis for this claim?

Well, the SNP under its new leader Nicola Sturgeon has explicitly said the party won't do anything that helps the Tories into power at Westminster.

However, the Nationalists have been careful not to rule out working with Labour if, as they hope, the SNP hold the balance of power at Westminster after the election.

That would probably mean what's known as a 'confidence and supply' arrangement where the SNP would allow Labour to form a government but not enter a formal coalition.

SNP Leader Nicola Sturgeon, whose party has explicitly said it won't do anything that helps the Tories into power Credit: PA

They'd demand a heavy price even for this. Far greater powers for Scotland and the 'end of austerity' - more accurately bringing down the deficit at a slower rate.

The SNP has also said it wants the cancellation of the replacement for the Trident nuclear weapons 'deterrent'.

What's the Labour view? They say that if their once loyal voters in UK elections switch to the SNP, as the polls currently suggest they might, that helps Mr Cameron stay in Downing Street.

As to coalitions, Labour simply won't go there. When I asked their Scottish leader Jim Murphy about the idea this week he said Labour's aim was to win an outright majority.

The most he would concede was that any talk of coalition - which he clearly hopes would not be necessary - would take place after the election result was clear.

Jim Murphy said any talk of coalition would take place after the election result was clear. Credit: Danny Lawson/PA Wire

But back to claim and counter-claim. In a mirror image of the Tory line, Labour today responded to the Prime Minister's speech with a social media video.

In it Ms Sturgeon is seen saying 'vote SNP' and it cuts to David Cameron applauding. It's taken from two different events, obviously, but it illustrates Labour's claim.

The video concludes with a picture of the Prime Minister with his hands joined, prayer-like, saying 'He wants you to vote SNP'.

Where does that leave the SNP? In a strong position. The only thing worse than being talked about by the Tories and Labour is not being talked about by them.

What we used to call the two big parties - a description no longer accurate in Scotland after the SNP membership surge - are trying to squeeze the Nationalist vote.

Labour hope the left-of-centre voters who backed a 'Yes' vote will come back to them and not transfer their allegiance permanently to the SNP.

The Tories are trying to appeal to the right-of-centre voters who voted 'Yes', emphasising the Conservatives claim the Nationalists are an old-style left-wing party.

For the Nationalists their core message is 'vote SNP and get a strong voice standing up for Scotland at Westminster'.

The crucial question is what will voters, especially those inclined to the SNP, make of all this? It'll be their call in the end.

At least the electorate know politicians care how they vote. The power lies with the people. That's democracy.