The SNP has claimed a coup against Labour by recruiting former trade union leader Jimmy Reid, veteran of the 1971 Upper Clyde shipbuilders work-in.
Former trade unionist Jimmy Reid has joined the SNP
Labour, who concentrated campaigning on council tax rebates for pensioners, said Mr Reid left the party years ago.
Conservative deputy leader Michael Ancram repeated his party's determination to save the Scottish regiments, which Labour plans to merge.
And the Lib Dems have been talking about scrapping the council tax.
Mr Reid, 72, achieved national fame when he led the Upper Clyde Shipbuilders to victory over government attempts to close their yard in 1971.
A former Labour election candidate, he accused the party of abandoning and betraying its founding principles.
Mr Reid said that the Nationalists adhered to the values that the Labour movement was based on.
"I have waited a long time to see forces emerging within the New Labour Party that would bring the party back to its roots, " he said.
Respected trade unionist
"But I have been waiting in vain and with every year that passes, Tony Blair and New Labour move further to the right. They are now indistinguishable from the Thatcherite Tories."
SNP leader Alex Salmond said: "The SNP is delighted to welcome Jimmy Reid as a member. He is not only one of Scotland's most respected trade unionists, he has also shown himself over many years to be a man true to his principles and those of the labour movement."
Lib Dems deputy leader Sir Menzies Campbell said Labour and the Conservatives had no solution to the ticking time-bomb of spiralling council tax bills.
He said: "Our proposals are based on the principles of fairness, efficiency, decentralisation, accountability and the experience of other countries where local income tax is tried and tested.
Peter Hain is highlighting the council tax rebate for pensioners
"Our figures are based on raising the same revenue as council tax.
"This is not, repeat not, a tax-raising measure."
In Scotland, any decision on whether to abolish the controversial council tax would fall to Holyrood, not Westminster.
Labour's Peter Hain joined Scottish Secretary Alistair Darling in Aberdeen to highlight the council tax rebate all pensioners are set to receive in the autumn.
Mr Darling said: "Labour is committed to delivering a £200 council tax rebate to every household with a member over 65, which pays council tax. This will be paid this year.
"In contrast, the Tories have been forced, because their sums do not add up, to cancel their promise of a council tax rebate for pensioners this year."
"We need more help for pensioners with additional aid for the poorest, we need to help older people to stay in work while they want to and we need to ensure that the public services older people rely on are properly funded. That will not happen if Michael Howard gets into Number 10 on 5 May."
Michael Ancram is backing the Save the Regiments campaign
The Conservative deputy leader defended his party's concentration on immigration in the campaign.
Mr Ancram said: "Michael Howard set out at the beginning of this campaign - as did the whole of the shadow cabinet - to deal with five key issues which we have identified as being the issues which are uppermost in people's minds."
The issues were hospitals, schools, police, lower taxes and controlled immigration.
Mr Ancram also attacked the UK Government over the decision to merge Scotland's infantry regiments into one super-regiment. "We reiterate our determination to save the Scottish regiments," Mr Ancram said.
"We think it's absolutely outrageous that at a time when our commitments overseas in the Balkans, Iraq and increasingly in Afghanistan over the next two years, are growing, that the government should effectively be abolishing Scotland's regiments."