The Labour leader will invoke the memory of his late Scottish predecessor when he addresses the Labour conference in Perth, warning independence would lead to Alex Salmond and the Conservatives competing to provide tax breaks for the rich.
Mr Miliband will seek to re-establish Labour’s credentials as the party of the Left, by contrasting his plans to tax the wealthy with the SNP leader’s reluctance to support his proposals to increase the top rate of tax from 45p to 50p.
In his speech, he will make a “positive” case for the Union, arguing people across the UK should work together to make a more prosperous country by redistributing wealth and creating more well-paid jobs. Outlining his vision for a successful UK, Mr Miliband will note that it is 20 years since the sudden death of Mr Smith, who was a driving force behind the establishment of the Scottish Parliament.
Regarded as one of the founding fathers of devolution, he was a great believer in keeping the UK. His untimely death from a heart attack in 1994 robbed Labour of one its brightest stars and paved the way for Tony Blair to take over.
Mr Miliband will say he was much admired for his decency and his belief in social justice, and that he is still mourned “across the country”.
“John Smith was a man who passionately believed in social justice in Scotland – and in the United Kingdom,” the Labour leader will say.
“Twenty years on, that flame of social justice still burns. And we can honour his legacy by winning the fight for Scotland to remain in the United Kingdom.”
Mr Miliband will argue that, under Labour, the whole UK can win a “race to the top” by pursuing his plans to tackle the “cost of living crisis” and build a better economy.
He will say his approach differs from that of the SNP, which is poised to join Prime Minister David Cameron in a “race to the bottom” that would see them compete with each other over tax breaks for the wealthy.
“Think how hard it would be to stop a race to the bottom happening if, on one island, we had a border running along the middle so we were divided in two. It would be two lanes in a race to the bottom – with David Cameron and Alex Salmond at the starting blocks – in which the only way they win is for you to lose.
“If Scotland was to go independent, it would be a race to the bottom not just on tax rates, but on wage rates, on terms and conditions, on zero-hours contracts, on taking on the energy companies, on reforming the banks. Those who can afford it will be paying less, while hard-working families across Scotland will pay more and see their services suffer.
“Alex Salmond, who claims to be a great social democrat, would end up running the same race to the bottom that the Tories have embarked upon. The SNP talk about social justice but they can’t build it – because they can’t be narrow nationalists and serve social justice at the same time.”
On the same day Labour delegates are expected to rubber-stamp the Scottish party’s new plans to extend devolution, Mr Miliband will say that bringing power closer to the people will strengthen Holyrood and help secure greater social justice.
He will voice his support of the proposals to devolve more income tax powers and benefits outlined in Scottish leader Johann Lamont’s devolution commission.
Its plans have been resisted by some in the party, who believe they have been driven by the SNP’s agenda. They have also come under fire from Nationalists, who say they don’t go far enough.
Mr Miliband will argue injustice could be tackled across the UK if Labour governments were voted into power at Westminster and Holyrood, saying: “A Labour government for the UK and a Scottish Labour government will be two governments working together on common challenges, not wrestling against each other, but never resting until we have built the more just and equal society that every part of the United Kingdom should be.”
He will underline his party’s commitment to taxing bankers’ bonuses, restoring the 50p income tax rate for earnings above £150,000, freezing energy bills until 2017 and ending exploitation through zero-hours contracts and failure to pay the minimum wage.
He will also emphasise his personal commitment to the Union by describing his own family’s links to Scotland – his father, Ralph, served with the Royal Navy at Inverkeithing during the Second World War – and talk about the shared history between Scotland and the rest of the UK.
SNP Westminster leader Angus Robertson said: “By a majority of two to one, people in Scotland believe that Labour have been damaged by ganging up with the Tories in the anti-independence campaign – which is two-thirds of people excluding ‘don’t knows’.
“Last month, it emerged that around a third of people in Scotland are now less likely to vote Labour because of their alliance with the Tories in trying to lay down the law to Scotland about our currency.”