Gordon Brown has warned that Nicola Sturgeon's plans would leave a £7.6 billion hole in Scotland's economy, as he pitched Labour as the country's "party of fairness and social justice".
In a letter to voters, the former Prime Minister claimed both the SNP and the Conservatives would leave the NHS at risk.
He said the nationalists would "scrap the Barnett formula, meaning that our NHS and other public services could only be funded by taxes raised in Scotland."
He also warned that the Conservatives were "committed to billions of pounds more austerity - which means less money for Scotland and our NHS".
In a speech later Gordon Brown is expected to say it is time to 'reset politics' beyond the 'old issues of constitutional change'.-
It is time to move beyond two years of constant talk of constitutional change to a new focus in the next two years on the social and economic change that Scottish people have said they want.
I am pressing the reset button because it is time to move beyond the old issue of bigger powers for the Scottish Parliament, as we now have more powers than at any time, to the issue that really concerns Scotland - better lives for the Scottish people.
The Kirkcaldy and Cowdenbeath MP is to address the annual meeting of Scottish Labour councillors in Glasgow this morning.
Gordon Brown hopes to "reset" Scottish politics in a bid to shift the focus from the constitutional debate to how to improve the lives of ordinary people.
Independence has dominated politics north of the border for the last two years ahead of September's historic referendum.
Former prime minister Mr Brown played a pivotal role in the campaign to keep Scotland in the UK and was also a key player in the pledge by the Westminster parties to deliver more powers for Holyrood.
Former prime minister Gordon Brown and key 'Better Together' campaigner is to announce that he is standing down as an MP, according to reports.
Mr Brown, 63, will soon confirm that he will quit at the general election in May, after playing a key role in the Scottish independence referendum campaign, sources have said.
The Labour MP has focused on charity work and his role as United Nations special envoy for global education since his resignation as prime minister in 2010.
An ally told the Sunday Mirror newspaper: "Gordon has confirmed to friends that he will stand down at the election in May.
"He wants to go out on a high after effectively salvaging the campaign to keep the UK together in September. He will focus on his charity work."
Mr Brown was first elected to Parliament in 1983 and was prime minister from 2007 to 2010 and chancellor from 1997 to 2007.
His last-minute intervention in the referendum debate was widely credited with helping the pro-union Better Together campaign to victory.
Gordon Brown will not enter the Scottish Labour leadership race, a source close to the former prime minister has confirmed.
Brown was tipped as a possible replacement for Johann Lamont after her resignation last week.
Some party members suggested Brown was a unifying figure, highlighting the work he did for the No campaign during the run-up to the Scottish referendum.
"For the past four years, and on every occasion he has been asked, Mr Brown has made it clear he is not returning to frontline politics, a source close to Brown said. That position has not changed."
Gordon Brown concluded an emotionally-charged speech at a 'No' rally by telling voters to "have confidence" and "stand up and be counted" at the polls.
On SNP promises about an independent Scotland, he said: "We've had no answers. They do not know what they are doing. They are leading us into a trap."
He pleaded with campaigners: "Have confidence and say to our friends, for reasons of solidarity, sharing, justice, pride in Scotland - the only answer for Scotland's sake and Scotland's future is vote No."
An impassioned Gordon Brown told supporters at a No rally that his concerns were not a fear of the unknown but instead "the risks of the known."
He described independence as an "economic trapdoor down which we go, from which we might never escape."
And he outlined the "real risks" of currency uncertainty, debt default, a lack of financial reserves, rising prices in the shops, rises in interest rates, threats to jobs dependent on trade with the UK - all of which, he said, were "unaddressed by the SNP."
Former prime minister Gordon Brown has accused the SNP of "perpetrating a lie" about protecting the NHS with independence.
The SNP has suggested the NHS is at at risk due to health policies in Westminster, but Mr Brown said the Scottish Parliament already has powers to protect the service.
Brown told a pro-Union event in Clydebank, "It is the SNP who are perpetrating a lie about what the NHS can and cannot do in Scotland."
The No campaign has seized on leaked documents that suggest the NHS in Scotland is facing a funding gap of up to £450 million and major changes will be needed.
Former prime minister Gordon Brown has addressed a Better Together campaign rally in Dundee:
Brown: "It's the fat cats who will benefit most from the SNP's tax policies, not the ordinary people of Scotland." http://t.co/6C00YZbCMf
Gordon Brown in Dundee: "Our UK welfare state offers better protection for pensioners, disabled and the unemployed." http://t.co/AYzvqu9EBH
Gordon Brown called on the international community to turn their offer of help to return over 200 schoolgirls kidnapped by Boko Haram 10 weeks ago into "practical measures".
The former PM said Nigerian authorities needed support with night-vision equipment, air cover and suggested some of the girls could be in neighbouring Niger, Cameroon or Chad.