As the issue dominated the debate for the sixth successive day, both sides appealed to less-well-off Scots, whose votes could determine the outcome.
Deputy First Minister Nicola Sturgeon said independence was the "opportunity of a lifetime" to ensure more Scots felt the benefit of the country's wealth.
The currency row has shown no signs of abating since it dominated last week's televised debate between First Minister Alex Salmond and the No camp leader Alistair Darling.
In the days that have followed, Mr Salmond has come under increasing pressure to explain how he would get around the pledge of the pro-Union parties to veto his currency union plans.
He refused to back down at the weekend, saying he would not settle for "second-best" and Scotland would continue to use the pound come what may. He also accused his opponents of a tactical mistake with their "kamikaze" vow not to enter a sterling zone with an independent Scotland.
Scottish Liberal Democrat leader Willie Rennie accused the First Minister of "self-righteous indignation" and implying others did not want the best for Scotland. "It is certainly not in the best interests of the people of Scotland to be kept in the dark on Alex Salmond's currency plan B."
Former SNP leader Gordon Wilson also called on Mr Salmond to change tactics to win the referendum, and "give people an economic reason for voting Yes".
In another blow, a new poll by Survation found a four-point increase in the No vote in the wake of Tuesday's debate, with No on 50 per cent, Yes on 37 per cent and undecideds 13 per cent. Taking out the "don't knows" puts No on 57 per cent, Yes 43 per cent.
A new No campaign poster showed a picture of Mr Salmond on a pound coin with the slogan "Is this your Plan B, Alex?"
Speaking yesterday in Kinning Park, Glasgow, Ms Lamont said: "I worry it will be the least who have the most to lose from separation. I believe this is the cynicism at the heart of the nationalists' offer. They are offering the most vulnerable in our society things which they know they cannot and will not deliver."
Vote yes, she said, for "less money to spend on schools and hospitals - on doctors and nurses."
Her comments follow those last week of Labour leader Ed Miliband, who claimed certainty over currency was necessary to deliver social justice in Scotland.
Ms Sturgeon accused the pro-Union parties of having failed to help the less affluent. Ahead of a visit to a Glasgow food bank today, she warned of what she described as the "gap between rich and poor under Westminster".
She added: "In an independent Scotland we will have an economic policy with full powers to put job-creation in Scotland first and to improve the quality of jobs available."
As the row over currency rumbled on, Labour leader Ed Miliband said at the weekend that the commitment not to enter a currency union would be contained in Labour's 2015 General Election manifesto, a move expected to be copied by the other main pro-union parties.
That stance came under fire from former Labour First Minister Henry McLeish, who predicted Scottish voters would react badly to the party's position that it would block a sterling zone.
Meanwhile, the Scottish Tories said Scots save as much as £4m a year on new school uniforms by being part of the UK.
The UK has an exemption from European Union rules, meaning it does not have to apply VAT to children's clothes, which the party warns could be lost if Scotland becomes independent.
* STV has received an apology from its online video partner, Brightcove, after some viewers struggled to watch Tuesday night's referendum debate through its STVplayer internet service. More than 1.7 million watched on STV with another 500,000 able to follow online.