SNP on a roll

Life moves slowly in the picturesque town of Annan, a few kilometers on the Scottish side of the border with England. A tractor trundles down the main street on a midweek morning, past solid terrace houses hewn of red sandstone. In the car park of a local shopping center around a dozen Scottish nationalist canvassers have gathered. It's not even 11:00 a.m. and they have already been out delivering leaflets and posters ahead of the UK general election on May 7.

In normal election times, Scottish National Party (SNP) candidate Emma Harper would have no hope in this part of Scotland. The nationalists barely scraped 10 percent of the vote here in the 2010 general election. But these are not normal times.

In Scotland, the center-left SNP are as much as 28 points ahead of Labour, according to opinion polls. Despite defeat in last year's referendum, the nationalists are predicted to win up to 54 of Scotland's 59 Westminster seats - a remarkable six-fold increase on their current representation. Such a result would make it almost impossible for Labour to win an overall majority in the UK, but could pave the way for a post-election deal with the SNP.

"The other candidates aren't at the races at all. We are the only optimists who want a better Scotland," says Harper, a flame-haired nurse who lives outside Annan. Metallic SNP and CND badges on her jacket twinkle in the bright morning sun.

Standing up for Scotland

The SNP is profiting from an unusual political alchemy: the party, in power in the devolved parliament in Edinburgh since 2007, is seen by many voters as competent and as standing up for Scottish interests. At the same, the SNP has become the party of protest for many fed up with established politics.

Across Scotland, the SNP's membership has quadrupled to over 100,000 since September's independence referendum. The Scottish nationalists are now comfortably the third-largest party in the whole of the UK. More than 3,000 people attended the party's spring conference in Glasgow last month.

In Annan, a local party branch was recently formed for the first time since the 1960s. The new chairman will be Henry McClelland, a businessman and chairman of the local football club Annan Athletic. McClelland is a firm believer in independence. He cried after Scots voted a margin of 55 to 45 to remain in the UK.

"The referendum isn't going to go away," he says. "There are going to be opportunities in the future. It won't go away."

On a roll

Despite the strong vote for the union with England in the Borders, the SNP's Harper is profiting from the energy unleashed by the referendum campaign. Many of her canvassers became politically active last year. Val is typical. Originally from England, she voted Labour for 35 years. Now she is firmly behind the SNP. "The Labour party has diluted, diluted until it is just a shadow of the Tory party," she says.

In Nicola Sturgeon the SNP also has the only UK political leader with a positive net approval rating. The 44-year-old former solicitor from Glasgow won plaudits for her performance in the only televised British general election debate featuring Prime Minister David Cameron.

On Thursday, Sturgeon will go head-to-head with opposition leaders including Labour's Ed Miliband in another live debate.

A strong performance in May's general election could put the SNP in a position to influence the next UK government. The party, founded in 1934, is likely to smash its previous best British election result, 11 seats in 1974.

Kingmaker for Labour?

The nationalists have ruled out going into coalition with Labour as long as Miliband's party supports the renewal of the Trident nuclear submarines, which are housed on the Clyde near Glasgow. But Sturgeon has kept open the possibility of a looser post-election pact with Labour to keep the Conservatives, who are politically toxic north of the Border, out of office.

Earlier this month, Sturgeon offered to form an anti-austerity pact with Labour if they have the seats to defeat the Conservatives, "regardless of which is the biggest party."

However, entering government in London could pose problems for the SNP, whose primary focus is Scotland and next year's elections to the devolved parliament in Edinburgh. The party has said it wants control of all taxes raised in Scotland - so-called full fiscal autonomy - but that demand is unlikely to be met.

"The SNP can't sign a blank cheque to Labour but they can't be seen to bring a Labour government down so they have to play a very careful hand," says Gerry Hassan, Scottish political commentator and author of The Strange Death of Labour Scotland.

The SNP's record high poll rating has fueled speculation of a second vote on independence. But nationalists are highly unlikely to hold another referendum until they know they can win, says Paul Cairney, professor of politics at Stirling University.

"The SNP won't win enough votes if they look like the independence party and nothing more and they have dealt with that problem well," says Cairney. "Long-term referendum chances hinge on them remaining a credible party of government in Scotland and, for now, a positive force in the UK."