Labour leader Sir Keir Starmer is to commit his party to delivering the “boldest devolution project in a generation”.
In a key policy speech he will say the Covid pandemic has put “rocket boosters” under the case for decentralisation of power.
He will promise “a positive alternative to the Scottish people” which aims “to preserve and renew the United Kingdom”.
Recent polls have indicated a majority in favour of independence in Scotland.
The SNP dismissed the plans as “constitutional tinkering” while the Scottish Conservatives said he was offering nothing new to challenge the SNP’s dominance of Scottish politics.
Sir Keir will use his speech on Monday to confirm the setting up of a constitutional commission, advised by former prime minister Gordon Brown, to deliver a “fresh and tangible offer” to the Scottish people.
“It is Labour’s duty to offer a positive alternative to the Scottish people. To show that you don’t have to choose between a broken status quo and the uncertainty and divisiveness of separatism,” he is expected to say.
“Boris Johnson isn’t Britain just as Nicola Sturgeon isn’t Scotland.
“The United Kingdom is much more than that, more than any individual. It has been before – and can be again – a great force for social justice, for security and for solidarity.”
Labour sources said the speech would set the tone for the party’s campaigning for next year’s elections to the Scottish Parliament as well as more broadly across the UK.
The party has not held power at Holyrood since 2007 and struggled to hold Westminster seats after being all but wiped out by the SNP in the 2015 general election.
With support for independence on the rise, Sir Keir will argue that the shared “history, values and identity” of the people of the UK mean there should be no place for internal borders.
The constitutional convention will also examine the wider balance of powers within the UK and how best to empower communities.
A letter last month signed by a group of leading Labour mayors in England called for more powers and funding for them to deal with Covid recovery.
In his speech, delivered remotely because of Covid restrictions, he will say he wants decentralising power from Westminster to be one of the hallmarks of the next Labour government.
He will insist his plans amount to more than shifting powers from one parliament to another, or transferring “a few jobs out of London”.
“There’s a yearning across the United Kingdom for politics and power to be much closer to people,” he will say.
The SNP’s deputy Westminster leader Kirsten Oswald dismissed Labour’s plans, saying the system was “broken” and “not working for Scotland”.
“No amount of constitutional tinkering of the kind proposed by Labour will protect Scotland from Brexit or the Tory power grab being imposed upon us against our will,” she said.
She said that even Labour supporters doubted their ability to oust the Conservatives from Westminster for another decade at least.
“It’s clear that only with the full powers of independence will we be able to properly protect our interests and secure our place in Europe – and that decision lies solely with the people of Scotland, not an out-of-touch Westminster system,” she said.
The Scottish Conservatives insisted they were the only party capable of taking on the SNP and championing the union.
Scottish Tory leader Douglas Ross said: “This isn’t leadership from Labour on the Union, this is the same old, tired argument that they’ve made before, and they’re offering nothing to challenge the SNP.
“Scottish Labour won’t work with unionist parties to stop the nationalists, and they won’t stand up to Nicola Sturgeon’s demand for another independence referendum as early as next year.
“Only the Scottish Conservatives have the strength to take on the SNP right across Scotland and the determination to stop their push for indyref2 again.”
The Scottish Liberal Democrats, however, said they are willing to work with Labour on a “third way” forward.
Scottish leader Willie Rennie said: “Liberal Democrats support a new federalist settlement that means we can find a better way to agree a common future across the United Kingdom.”