Fife Council leader Peter Grant is the SNP's candidate in the by-election
First Minister Alex Salmond has challenged Gordon Brown to a head-to-head debate in the run-up to the Glenrothes by-election.
As he launched the SNP campaign for the seat, Mr Salmond predicted the nationalists would pull off a shock in the vacant Westminster seat next month.
The SNP leader was joined by the party's candidate for the seat, Fife Council leader Peter Grant.
The Nationalists are hoping to overturn a Labour majority of 10,500 to win.
The SNP overturned a Labour majority of 13,500 to win Glasgow East in the summer.
Mr Salmond said: "I detect that the political earth is still shaking from Glasgow East and it's going to be felt next here in Glenrothes."
However, The BBC has learned that Gordon Brown has been told that Labour will win the Glenrothes by-election.
The BBC understands that campaign strategists - who just three weeks ago were warning the prime minister that Labour would lose -- have now told him that the tide has turned in the constituency, partly the result of Mr Brown's handling of the banking crisis.
On a visit to the constituency, Mr Salmond said rising energy costs would be among the key issues in the campaign and predicted action in these areas as "the political pressure mounts".
He also reiterated his weekend calls for a £1bn package from Westminster to help reflate the Scottish economy, including £120m held by energy watchdog Ofgem for Scotland.
And he welcomed Mr Brown's plans to campaign in the constituency: "Battle will be joined and the issue will be toe-to-toe.
"I'll be delighted to meet Gordon on the campaign trail - I would be delighted, incidentally, to debate with the prime minister."