The SNP launched its election campaign yesterday with a claim by leader Alex Salmond that Labour was facing not just defeat but "absolute calamity".

Buoyed by a second day of good newspaper poll results, the Nationalists' biggest enemy will become complacency, such is the spring in their step as they enter the uncharted territory of sustaining a lead into the final month of campaigning.

Labour, in contrast, tried to turn the sombre polling figures to their advantage. Visiting a school construction site in Midlothian with Communities Minister and local MSP Rhona Brankin, Jack McConnell said: "The polls are a wake-up call to Scotland.

"They are a call to the people of Scotland to realise how serious is the threat of the SNP - and how important it is that they come out and vote and back Labour to build up Scotland for another four years."

SNP MSPs and their staff walked out of the parliament as it closed for business yesterday afternoon and marched across town to join other party candidates at a hotel to hear a rallying call from Mr Salmond.

A Daily Mail poll conducted by Scottish Opinion gave the SNP a six-point lead over Labour - by 34% to 28% - in the constituency vote, and a 32% to 28% lead in the regional list vote. While down on the even bigger leads - 10 points and five points respectively - recorded by Populus for the Times the previous day, these polls still represent unprecedented figures for the SNP so close to an election.

Mr Salmond claimed that the reason for this was the negativity of the Labour campaign and the way in which on key issues such as Trident, a share of oil wealth and more powers for the Scottish Parliament the SNP was running with the grain of Scottish popular opinion.

"If the Labour Party keep running this campaign they will go down not just to defeat but to absolute calamity," he predicted. "Scotland is in the process of independence and will become independent when the people so choose."

He said unionists believed they could contain the independence, using devolution to "kill nationalism stone dead".

But he said: "You cannot put boundaries on the march of a nation."