Labour leader Ed Miliband will today pledge to take the positive case for the Union directly to Scots between now and the independence referendum.
In a speech to the Scottish Labour conference in Perth, he will tell delegates that arguing for the benefits of the UK would win the vote.
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And he will say that co-operation between Scotland and the other parts of the UK is the best way to achieve social justice north of the Border.
His speech comes as Coalition sources indicate that they plan a new phase of positive campaigning.
A senior Whitehall source said that repeated attacks on independence, dubbed the "Dambusters' strategy", had been judged to be effective, but there was a growing view the approach had been too negative.
Instead, he said, there had to be an "injection of love" for Scotland.
Earlier this week former Liberal Democrat leader Charles Kennedy called on those arguing for a No vote to be more positive, a view echoed by Tory backbencher Guto Bebb.
The SNP has long accused the pro-Union parties of running a negative campaign, dubbed "Project Fear".
In his speech Mr Miliband will argue that Scots can win a "race to the top" as part of the UK.
In what has been described as a deeply personal address, he will also highlight his own links to Scotland, including the fact his father trained in Inverkeithing while serving with the Royal Navy during the Second World War.
And he will say, under independence, First Minister Alex Salmond and Prime Minister David Cameron would embark on a damaging competition to offer the most tax breaks to the rich.
"The SNP want to tell you that there is a progressive Scotland and a Tory England," he will tell party faithful.
"There isn't. There are millions of people across every part ... who want to be part of a country that is more just, more equal, more fair.
"Let's rebuild all of our country in the cause of social justice. Together, not alone; as neighbours on this island, not as strangers; as friends, not as competitors; in a race to the top, not to the bottom."
He will suggest independence would leave David Cameron and Alex Salmond on the starting blocks of such a race "in which the only way they win is for you to lose".
In a conference curtain-raiser last night, former Prime Minister Gordon Brown claimed that Scotland's low and middle-income families would be better off to the tune of £1.4 billion under a Labour administration at Holyrood compared with an SNP government in an independent Scotland.
Johann Lamont, the Scottish Labour leader, will address the conference tomorrow.
At Holyrood yesterday she condemned Nationalists for refusing to support calls to make all firms accepting government contracts pay their workers the living wage. It followed a row last week when Nationalist MSPs blocked a bid by Labour to include the proposal in legislation going through the parliament.
The voluntary living wage is £7.65 per hour, compared with the minimum wage of £6.31.
Speaking at First Minister's Questions she said the move would help 400,000 Scots.
Mr Salmond said his party had an "impeccable" record, having enforced the living wage for Scottish Government employees.