Former Prime Minister Gordon Brown will today propose six "major" constitutional changes to revamp the UK's relationship with Scotland, in a key speech outlining his vision for the country within the Union.
Mr Brown will argue his plans for a new power-sharing constitutional partnership between Scotland and the rest of the UK represent a "radical break" from the status quo and a more appealing offer than "irreversible" independence.
Such a view of Scotland's future represents a "clear, positive alternative" to independence, and is one which will deliver a strong Holyrood and enable the country to meet the challenges of poverty, health inequality and poor educational standards, it is claimed.
The Fife MP for Kirkcaldy and Cowdenbeath is expected to say: "I want to move us from the old highly-centralised, uniform Britain dominated by out-of-date ideas of an undivided Westminster sovereignty to a new diverse power-sharing, risk-sharing, resource-sharing UK which is best defined not as an old union but as a modern, constitutional partnership of nations."
Mr Brown will outline his plans to an audience in the east end of Glasgow later today.
The former Prime Minister and Chancellor has spoken out on issues surrounding the independence debate in the past.
He has previously called for legislation to make the Scottish Parliament a permanent and irreversible part of the how Britain is governed, and proposed a written constitution to highlight the importance of pooling resources across the UK.
But he said he was entering the nationwide debate on Scotland's future from today "because a moment cannot now be lost in detailing the positive case for a strong Scottish parliament in a strong Britain".
The six pillars of his plan are:
:: A new UK constitutional law - backed by an historic document equivalent to a bill of rights - to set out the purpose of the UK as pooling and sharing resources for the defence, security and well-being of the citizens of all four nations, including a commitment to alleviate unemployment and poverty.
:: A constitutional guarantee of the permanence of the Scottish Parliament, backed up by a constitutional lock that prevents it being overruled or undermined.
:: A new division of powers between Scotland and Westminster that gives Holyrood more powers in employment, health, transport and economic regeneration.
:: A new tax sharing agreement that balances the commitment of the UK to pool and share its resources with the need for accountability to the electors in all the places where money is spent.
:: New power-sharing partnerships to address shared problems on poverty, unemployment, housing need and the environment which, Mr Brown argues, cannot be addressed unless the Scottish and UK governments work together.
:: A "radical" transfer of powers downwards from Westminster and Edinburgh to local communities.
Mr Brown's plan is to be submitted to the Labour Party's devolution commission and the party's Scottish leader, Johann Lamont.
It would, he says, force Britain to change and lead to a revamp of the UK's relationship with Scotland, and is "a far bigger, more modern, more forward looking - and ultimately more appealing - idea than that of a wholly separate state".
Mr Brown is expected to say: "The majority of Scottish people do not want separation but equally they do want change, not the status quo. It is now six months from the referendum and time to enact that change.
"If people are asked to support the Union it is crucial that people know what the purpose is and it is no longer left unstated and unexplained.
"We need to draw up a statement of purpose, that we pool and share resources and risks for the benefit of all. A new constitutional settlement should reflect a modern purpose, meaning and aspiration for the United Kingdom. The purpose of the Scottish Parliament should be to use the maximum devolution possible, consistent with our desire to share resources equitably across the UK.
"To create this new power-sharing constitutional partnership we must bury for good the notion that Westminster enjoys undivided sovereignty over the country and reject the idea of Britain as the old unitary centralised state of the constitutional textbooks.
"The purpose of a reformed United Kingdom should be to provide a strong and sustainable basis on which to tackle the unparalleled challenges of the times we live in, including the pooling and sharing of our resources for the delivery of opportunity and security for all."
A spokesman for the pro-independence Yes Scotland campaign said: 'It's been a long time since the UK was genuinely about pooling and sharing resources. Under successive Labour and Tory governments, Westminster policy has consisted of an ever-increasing concentration of wealth and job opportunities in London and the south-east, and a growing gap between rich and poor.
"We agree with Gordon Brown that the purpose of constitutional change must be to empower people. We also agree with him that Labour and the other anti-independence parties need to spell out what further powers they will guarantee in the event of a No vote. But we have heard such promises before and they came to nothing then and they'd come to nothing again. Labour and the Tories cannot even agree among themselves what further powers should be devolved to Scotland.
"The only way to guarantee the powers people want and Scotland needs is to vote Yes on September 18.
"Nobody, whether they favour a Yes vote or a No vote, should be in any doubt that if we reject independence in September we will pay a very heavy price - more Tory governments that we don't vote for, more austerity and more attacks on those who can least afford it."