The Prime Minister is expected to sign a deal with Scotland's First Minister today granting Holyrood the power to hold a historic referendum on independence.
David Cameron will meet Alex Salmond in Edinburgh following months of negotiations about the ballot, expected to be held in autumn 2014.
Private meetings between the two governments have covered contentious issues about the question on the paper, expected to be limited to a single Yes-No option.
Proposals for a second question on further devolution, short of independence, were firmly opposed by the UK Government.
The referendum is expected to be open to 16 and 17-year-olds as supported by the Nationalists.
Today's landmark event will determine a technical measure known as a Section 30, which passes power from Westminster to Holyrood to legislate on the referendum.
Cameron, Tory leader, has pledged that keeping the United Kingdom together is his number one priority.
In a speech later today he will say: "This marks the beginning of an important chapter in Scotland's story and allows the real debate to begin.
"It paves the way so that the biggest question of all can be settled: a separate Scotland or a United Kingdom? I will be making a very positive argument for our United Kingdom.
"It is now up to the people of Scotland to make that historic decision. The very future of Scotland depends on their verdict. It is that important. This agreement delivers the people's referendum."
Salmond secured a mandate to hold the referendum by winning an unprecedented majority with his Scottish National Party at Holyrood last year.
He said: "The people of Scotland gave the Scottish Government a clear mandate in last year's election to hold a referendum on Scotland's future in 2014.
"The agreement I expect to reach with the Prime Minister is one which ensures that not only is the referendum made in Scotland, but that the fundamental right of the people of Scotland to choose their own future is respected by all.
"The agreement will see Scotland take an important step toward independence, and the means to create a fairer and more prosperous Scotland. I look forward to working positively for a yes vote in 2014."
The campaign picked up pace in February with a visit from the Prime Minister, followed by the formal launches of the pro-independence Yes Scotland and pro-Union Better Together cross-party movements.
Negotiations between the governments have been led by Deputy First Minister Nicola Sturgeon and the UK Government's Scottish Secretary Michael Moore.
The most recent poll on independence suggests support for leaving the UK has dropped.
A survey of 995 adults, published last week, showed support for the Union at 53% compared with support for independence at 28%.
But, according to the latest YouGov poll of 1,000 people commissioned by the SNP, 64% of respondents said they thought the Scottish Government was better at making decisions for Scotland than the UK Government which received 24%.