General Election 2010: Will SNP pay price of a tactical anti-Tory vote?

The French sculpture's classic image of intellectual inquiry, albeit now appendaged with an appetising snack, makes a fitting backdrop to political discussion. While the counter sign reads "lentil or minestrone", the voters in Glasgow Central are torn between "Labour or SNP".

During the 2007 Scottish elections the SNP made a series of gains in traditional Labour heartlands. Dundee West, Fife Central, Stirling and Kilmarnock all fell under the sway of the Scottish Nationalists, while Glasgow Govan, which comprises a chunk of the Westminster constituency Glasgow Central, was won, on the third attempt, by Nicola Sturgeon who overturned a 1,235 majority.

Yet the question remains, will those SNP voters fade away as their attention focuses on the reality of a straight choice between a Labour or Conservative government? Not if you are Linda Johnson, the owner of the Kinning Perk, who voted Labour during the previous general election but has since become a convert to the SNP.

"I'll still be voting SNP," said Johnson without hesitation. "Nicola Sturgeon and her team genuinely help. You call her and she calls back." Pointing to the scaffolding outside the window she said: "The roof is getting repaired because of the SNP." So the goodwill gathered by Sturgeon will now be bestowed upon Osama Saeed, the SNP's Westminster candidate.

According to his opponent, Anas Sarwar, the SNP will require all the goodwill it can muster as their voters are defecting. "The message is getting across that the key battle is between a Labour and a Tory government and the people of Scotland do not want to see a Tory government. We've spoken to hundreds of people who voted SNP or Lib Dem in 2007 but will be voting Labour in this election."

The situation hasn't been helped by the decision of Brian Souter, one of Scotland's richest men and a stalwart SNP donor, to keep his powder dry and his cash in the bank until the next Scottish Parliamentary elections. As John Curtice, professor of politics at Strathclyde University, explained, Souter is not alone in viewing Westminster elections as different.

"We know from every opinion poll that has ever been conducted in Scotland on this subject during the last 12 years that people are less likely to vote SNP in Westminster elections than they are in Scottish elections. If you ask people what they are voting for, they tend to say what is going on in Scotland, and then for the Westminster elections they are looking to see who will make the best job of running the UK as a whole. People ask themselves different questions. If we look back at 2005, the SNP had a disastrous election."

Whatever the question, candidates are stomping the streets in a bid to assure Labour voters that the answer is still SNP. In Ochil, back in 2007, the SNP claimed the seat by 490 votes and Annabelle Ewing is now intent on taking the Westminster constituency, which will mean overturning a slim Labour majority of 688. While in Dundee West, Jim Barrie, the convener of the SNP led city council, also hopes to nurture recent party success in the city and win the seat for the nationalists.

In Kilmarnock and Loudoun, George Leslie, a local vet and SNP member for 45 years, is anxious to swipe the seat away from Labour just as Des Browne, the former Cabinet minister, retires.

Back in Glasgow Central Robert Adams, 49, who is unemployed, is swithering. "I don't think Gordon Brown is doing a particularly good job, but I also don't think the SNP will do anything. It is a national election and it's strange to see Alex Salmond so vocal when he is not even standing as a Member of Parliament. I may just go for Labour."