Mr Salmond said the System Three poll in The Herald newspaper, which suggested the SNP had closed the gap on Labour, vindicated his recent decision to re-focus the party's campaigning strategy and go out "on the streets".

However, both The Herald poll and a larger survey in the Daily Record indicated neither Labour nor the nationalists would achieve an outright majority on 6 May, fuelling the possibility of a coalition administration involving a smaller party.

Alex Salmond was challenged over SNP spending plans

The Labour hierarchy played down the significance of the latest Herald poll which indicated the SNP jumped seven points in both the first past the post and regional votes to 33% and 34% respectively while Labour dropped two points in the first vote (44%) and three in the second (37%).

Labour, the Scottish Liberal Democrats and Scottish Conservatives spent Thursday attacking the Scottish National Party over the alleged cost of independence.

But Mr Salmond focused on party performance and said the tide was turning for the nationalists after his pledge that activists would get their "jaickets off" after falling poll ratings last week.

He said: "I think there is all to play for in this election. I think our political opponents are starting to get very worried with the SNP becoming the 'comeback kids'.

"I'm not basing our campaign on opinion polls, I'm basing it on a message I think is attractive to the people of Scotland."

But Chancellor Gordon Brown chose to highlight the SNP's spending proposals and said voters would not be fooled by the nationalists' empty promises.

Colin Blane reports from the "forgotten corner of Scotland"

He said: "They must spell out the true cost of jobs and spending, for a separate army, navy and air force. Separate embassies and consulates. A separate social security system - all disrupting established links with the United Kingdom, which is Scotland's biggest market for exports."

The onslaught continued under the Liberal Democrats and Treasury spokesman Malcolm Bruce said he had found a "black hole" in the nationalists' "Penny for Scotland" plans.

Mr Bruce said: "I don't think it is very intricate to say to people a penny on income tax will yield £230m when the House of Commons Library can easily confirm that it will yield £215m. That's not complicated at all.

"What that tells you is the SNP can't even calculate what the basic effect of a penny on income tax yields to the people of Scotland."

And Scottish Tory leader David McLetchie said the SNP economic blueprint will amount to little more than a continuation of their "deliberate attempt to lead the electorate up the economic garden path".

Mr McLetchie said the SNP "Penny for Scotland" was a penalty for being Scottish.