Tony Blair and Gordon Brown are expected to team up to campaign against the SNP in the Holyrood elections.
The prime minister was interviewed by BBC Radio Scotland
The prime minister and the chancellor will set out Labour plans on education and accuse the SNP of creating risk and uncertainty with independence plans.
SNP deputy leader Nicola Sturgeon said their presence would be an "own goal".
The Tories are promising pensioners a 50% council tax discount and the Lib Dems will set out plans to repeat their Dunfermline by-election success.
The Libs Dems took the Dunfermline and West Fife seat Westminster seat just over a year ago.
Willie Rennie won the seat by 1,800 votes, overturning an 11,500 Labour majority at the 2005 election.
Scottish Lib Dem leader Nicol Stephen will outline the party's plans to replicate the "stunning success" of the Dunfermline by-election across Scotland.
The prime minister and the chancellor are expected in Glasgow
The prime minister and the chancellor are expected in Glasgow to set out Labour's economic case against independence on the first official day of the contest.
The Scottish Parliament was formally wound-up at midnight, signalling the official start of the election battle.
The SNP deputy leader said: "A joint appearance by Tony Blair and Gordon Brown must be Labour's biggest own goal yet of the campaign."
Ms Sturgeon said: "We know that Mr Blair is a major electoral liability for Labour as the man who took the country into an illegal war.
"And now Gordon Brown's appearance will mire Labour's campaign in the pensions crisis."