THE SNP gathers in Glasgow today for its biggest ever conference. Around 3000 people will be at the SECC, a measure of the party's extraordinary success since its defeat in last year's independence referendum.

The slogan that will projected onto the big screens and beamed into people's homes when Nicola Sturgeon makes her keynote address this afternoon is "Stronger for Scotland". The scenario the SNP wants to implant in voters' minds is simple and it is not going to change between now and May 7: a large bloc of SNP MPs will mould a minority Labour government into something better than it would have been, limiting spending cuts, delaying the replacement of Trident and pressing for further devolution. Polls suggest that is an outcome a great many Scots would welcome. The SNP's long and sustained effort to portray itself as a more progressive party than Labour has, despite some large question marks over the accuracy of the picture, paid off. The referendum has also served the Nationalists well. The intense debate about Scotland's continued place in the UK has changed the way many people think about their politics. As Professor John Curtice noted this week, many are not considering this General Election in terms of who would best govern the UK but who would best represent Scotland. On that score the polls are clear: the SNP is way out in front.

This is the almost impossibly strong position the SNP finds itself in this weekend. On the ground, the party's 100,000 members are making their presence felt, delivering 10million leaflets since the start of the year. Perhaps the biggest problem for Ms Sturgeon is ensuring the conference does not become a victory party six weeks out from polling day. "We're taking absolutely nothing for granted," pleaded Westminster leader Angus Robertson a little unconvincingly, as he brandished the latest YouGov party leader approval ratings with a triumphal flourish. They showed Ms Sturgeon on plus 33 per cent, David Cameron on minus 36 and Ed Miliband on minus 53.

In constituencies across Scotland, Labour and the Lib Dems face being crushed by the SNP steamroller. Only the Tories are smiling, knowing every SNP gain from Labour increases their chances of emerging with most seats across the UK and, as a result, the first chance of forming a government if we are heading for a hung parliament. If the numbers allow, a second Con-Dem coalition should not be discounted.

Labour yesterday issued a campaign new video, a mashed up montage of news footage telling a story of SNP victories in Scotland and David Cameron driving into Downing Street on May 8. "Vote SNP get Tories," was the pay-off. Like the SNP's pitch it's not going to change, but will it change anyone's vote? It hasn't shifted the polls so far.

The truth is, this election looks win-win-win for the SNP.

The Nationalists are confident Mr Cameron's return to No. 10, with minimal support from Scotland, would increase demands for independence. Alex Salmond's frequent media appearances in London, talking up his party's chances of "holding the power" and bouncing Labour to the left, have fuelled an effective Tory scare campaign down south. Ms Sturgeon will issue the same message today, albeit couched in softer language. Labour's Douglas Alexander has openly accused them working to "drive up the Tory vote" in pursuit of independence.

In the unlikely event of a confidence and supply deal - a formal alliance though looser than full coalition - between Labour and the SNP, Jim Murphy's Scottish Labour would be left high and dry. How could it oppose the party it was working with at Westminster when we come to next year's Holyrood elections?

If the SNP end up supporting a minority Labour government on a vote by vote basis, as Ms Sturgeon expects will happen, the SNP would claim credit for any small concessions but continue to hammer Ed Miliband. SNP MPs would keep him propped up so SNP MSPs could take pot shots at him at Holyrood. Labour's planned cuts may be on nothing like the scale of those outlined by George Osborne but "Labour's cuts" would become a constant refrain at Holyrood. It would be deeply damaging for Labour.

In short, it's hard to see how the SNP can lose if they do even nearly as well as the polls suggest. This might not just be its biggest ever conference, it might be its best.