For the past few elections, general and Scottish, I have voted Labour.

I am not a paid up member of that party - far from it, although I like both our local Labour MP and MSP and think they do a good job.

The reason I vote for them is because in my part of Scotland, Labour has the best chance of beating the Nationalists. I would happily vote for a LibDem or a Conservative candidate if I thought they were the only way of stopping the SNP, though I'd draw the line at someone on the outer edges, say from the Greens or Ukip.

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It is not uncommon to vote tactically. In fact, there were many people (some of them Tories) who voted the Nationalists into power for the first time in the 2007 Scottish election simply to get rid of the tired Labour/LibDem coalition, and again in 2011.

Now, there are moves afoot to use the ploy in May's general election to stop the separatist surge, with a cross-party campaign being launched this week. Set up by former No activists, business figures and academics, the Scotland in Union group will identify constituencies where tactical voting could help defeat the SNP.

The group says it won't tell people how to vote but will offer advice in seats where traditional Conservatives backing Labour, or vice versa, could ensure a pro-Union victory.

Naturally, no major political party will endorse such a movement; the Westminster ballot is not supposed to be a re-run of the independence referendum, when the Unionist parties forgot their differences to curb a common foe.

David Cameron, and the Scottish Tory leader Ruth Davidson, said Scots must vote Conservative to keep Ed Miliband out of Downing Street. And Ed Balls was in Scotland last week telling people if they didn't vote Labour they'd get the Tories.

But supporters of the main parties can do what they want, and what many of them seem to want most of all is to see off the SNP. Scotland in Union says it has anecdotal evidence of voters throughout the country considering voting tactically to stop the Nationalist bandwagon.

And what a bandwagon it is. The most recent opinion poll, for TNS last week, put the SNP on 46 per cent of the vote, up five points since last month, with Labour down one point to 30 per cent.

Nicola Sturgeon, SNP leader and First Minister, said the Westminster parties are "spooked" by the Nationalist threat, which could see her party with as many as 40 seats, a big improvement on their current six.

And she said if the Westminster establishment is worried about the headline polls, it should be equally concerned by the SNP's private polling, which tells "exactly the same story".

But we should remember the Yes campaign's private polling last year predicted a sure win for independence, and that, as we now know, was wide of the mark.

The fact the Nationalists don't accept the referendum result, and won't acknowledge the clear will of the majority, is the impetus behind the new campaign for the Union.

The independence battle took a lot out of Scotland. It went on for years - is still going on - and brought bitter divisions to the country. And it disrupted the business of government to the extent that there has been no progress in the delivery of public services. Important reforms in education and health have had to take a back seat while ministers and their civil servants obsess over the constitution.

Scotland had enough last September and voted to stay in the Union. The thought of another referendum - which, whatever Ms Sturgeon says, is the only reason the Nationalists are angling for influence in Westminster - is too ghastly to contemplate.

Anything that puts paid to secessionist ambition is to be encouraged, even if that means handing Mr Miliband, possibly the most unsuitable prime minister material since Michael Foot, the keys to Number Ten.

For many of us in Scotland, saving the Union is more important than the success of any party. Once this might have felt unprincipled but, despite Mr Miliband's courting of the Left, the policy differences between the main parties are not so great - or not as great as the chasm between the Nationalists and everyone else.

For Unionists, loyalty to a particular party must come second to loyalty to Britain, the preservation of which has been catapulted to the top of the political agenda in Scotland in the years since the last general election in 2010.

Scotland in Union admits tactical voting is not for everyone but there is one constituency where perhaps it should be: Gordon.

"A lot of people are looking at Gordon as, not a bell weather, but a totemic struggle," said the man behind the new Unionist group, Alastair Cameron, a former captain in the Highlanders.

Gordon is the north east seat being contested by Alex Salmond, who hopes to dislodge the LibDems. He will have to overturn their majority of almost 7,000 but it is widely expected, not least by him, that he will prevail.

The LibDems have an unseasoned candidate, replacing the Commons veteran Sir Malcolm Bruce, and the opposition to Mr Salmond is split.

Yet this was very much No territory in the referendum - with voters there rejecting independence almost two to one - and there is little doubt that if the Unionist parties could agree to a tactical voting strategy they could humiliate the former SNP leader (so confident of winning that he has been offering himself as a deputy prime minister to the highest bidder).

There are other key seats, targeted by the Nationalists, where the combined force of the pro-Union parties could be effective. During the referendum, it wasn't only the Yes camp who teased out a reluctant electorate.

No activists, too, managed to appeal to people who, disillusioned by partisan politics, hadn't voted for years. Faced with Britain's break-up, they suddenly found a cause close to their hearts.

That cause remains central to the election in Scotland and if the same canvassers descended on the same wards, with much the same message, they might succeed in bringing more people to the ballot boxes than the Tories or Labour or the LibDems by themselves.

The SNP has been quick to pour scorn on the anti-independence alliance, with the party's Westminster leader Angus Robertson saying it would prove disastrous for Labour if it was seen to be joined at the hip with the Tories again.

But for whom would it be most disastrous? The Scottish Conservatives, who have just one Westminster seat, are not realistically hoping to gain much more. If there is widespread tactical voting, it is largely their traditional voters who will be holding their noses as they mark their ballot papers for Labour candidates.

It is a price many think is worth paying. The vote on September 18 should have been final but was treated as a dummy run by the Nationalists.

Their assault on the British parliament they seek to destroy may be cynical in the extreme, but they have become the party to beat in Scotland. If that takes a united front, let's unite.