In a speech to the SNP spring conference, Nicola Sturgeon, Scotland's deputy first minister, said independence would allow Labour supporters to take back control of a Scottish party that had become a “pale imitation” of the Conservatives and was “dancing to a Westminster tune”.
Ms Sturgeon's comments underscore SNP efforts to broaden support for a yes vote in September's referendum beyond traditional nationalist supporters – a task made more urgent by opinion polls that suggest a narrowing of the no camp's lead may have stalled.
Strategists say concern about the consequences of continued UK government by the Conservatives, who are deeply unpopular in Scotland, could attract formerly Labour voters.
Ms Sturgeon said she had joined the SNP in the 1980s because of the damage she saw being done to her community by a Conservative government under Margaret Thatcher that was not supported by Scottish voters.
“Nearly 30 years later, the fabric of our society is again under threat from a government that has no mandate in Scotland,” she said, adding that even when Labour governed the UK, Scottish priorities did not prevail.
“For everyone out there with Labour in your heart, the message is clear: don't vote no to stop the SNP, vote yes to reclaim the Labour party,” Ms Sturgeon said.
The SNP's spring conference, which marks the 80th anniversary this week of the party's founding, is its last full gathering before the September 18 referendum and an important chance to build momentum for the yes campaign.
However, opinion polls out in the past few weeks suggest that a narrowing of the pro-union lead since the Scottish government released its vision for independence in November could have petered out, with the nationalists still trailing.
“The progress that the yes side made during the winter may, for the time being at least, have come to a halt,” said leading psephologist John Curtice.
Analysts say about a third of voters who backed Labour in the last election to the Scottish parliament may vote yes and SNP strategists see promoting the social benefits of leaving the UK as a way of attracting more.
In speech greeted with enthusiasm by a full hall of party faithful, Ms Sturgeon stressed the SNP's commitment to softening the impact on Scotland of Conservative welfare cuts, opposing privatisation in the National Health Service and maintaining free university education.
Pro-union campaigners say Scotland's devolved government already has considerable powers to set its own social policies and would gain more if it votes no in September.
A poll released on Friday by Better Together, the cross-party campaign against independence, highlighted the potential benefits fokr unionists of persuading voters that defeat for the nationalists would pave the way for more devolution.
The survey, carried out by YouGov, found that 57 per cent of voters would back Scotland remaining in the UK with increased powers for the Scottish parliament, while 35 per cent would prefer full independence.
When YouGov last month asked voters their view on independence, without mention of more devolution, the no camp lead was narrower at 52 per cent to 37 per cent.