Major figures from Scotland's main political parties have taken part an election debate for TV in Edinburgh.
Tony Blair and Gordon Brown are expected to team up to campaign against the SNP in the Holyrood elections.
Scottish Labour leader Jack McConnell faced SNP chief Alex Salmond, Lib Dem leader Nicol Stephen and deputy Tory leader Murdo Fraser at the hustings.
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.
The event was organised by Sky News and the Sunday Times.
SNP deputy leader Nicola Sturgeon said their presence would be an "own goal".
Last month the SNP accused Mr McConnell of being scared to join a debate. The Labour leader said he wanted to challenge Mr Salmond on independence.
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.
Mr McConnell said devolution had "matured" over the past eight years.
Economic case
Policy by policy
The Libs Dems took the Dunfermline and West Fife seat Westminster seat just over a year ago.
He said the Scottish Executive coalition between Labour and the Liberal Democrats had been the right way to bring stability to devolved government.
Willie Rennie won the seat by 1,800 votes, overturning an 11,500 Labour majority at the 2005 election.
But he added that after the Scottish Parliament elections on 3 May it could be the case that the largest party tries to govern without an overall majority on a "policy by policy, bill by bill" basis.
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 SNP leader clashed with Mr McConnell over his reasons for discounting independence.
The prime minister and the chancellor are expected in Glasgow
Mr Salmond said: "The arguments that Jack deploys are identical to the arguments that the Tories used to deploy on devolution."
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.
There were heated clashes between Alex Salmond and Jack McConnell
The Scottish Parliament was formally wound-up at midnight, signalling the official start of the election battle.
Mr McConnell responded by saying that devolution and independence could not be compared.
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."
He said that there was never a proposal under devolution for Scotland to have "a separate currency, a separate Scottish membership of the European Union and to break Scotland away from the rest of the United Kingdom".
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.
The Labour and SNP leaders then started talking over each other, and the din ended with Mr Salmond telling his adversary: "Your argument two minutes ago was uncertainty.
"And now Gordon Brown's appearance will mire Labour's campaign in the pensions crisis."
He said: "The Tories used the same argument. They were beaten then and you will be beaten now."
Sniff of power
The debate also saw the Scottish Lib Dem leader spell out his party's stance on an independence referendum.
"If there is a majority in the parliament after 3 May for parties in favour of independence, of course they can proceed to the next step as they want to deliver independence, and that's through a referendum," Mr Stephen said.
"But the Liberal Democrats don't believe in independence and we don't support a referendum - and can you think of a single party or government which promoted a referendum on an issue it doesn't support?"
But he faced a taunt from the Tory deputy leader that Lib Dems were political "prostitutes".
"They are the party who in the past tended to ditch every principle for a sniff of power," Mr Fraser said.
"I just hope you are prepared to stick to your guns on this."
