David Cameron and Alex Salmond will today sign off on a historic deal to hold a single question referendum on whether Scotland should remain in the United Kingdom.
Under plans to be formally agreed by the Prime Minister and First Minister at a meeting in Edinburgh voters will be asked a single yes/no question in the independence plebiscite and the Scottish Government will be able to extend the franchise to those aged 16 or over.
The deal sets the stage for a marathon campaign ahead of the vote which will not be held until in the autumn of 2014.
Under the terms of the agreement the Scottish Parliament will have the power to formulate the exact phrasing of the referendum question.
However this will then go to the Electoral Commission which could amend it if it is considered unclear or biased in one direction. The Electoral Commission will also set funding limits for each campaign.
"This marks the beginning of an important chapter in Scotland's story and allows the real debate to begin," Mr Cameron is expected to say. "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."
The latest polls on independence suggest that support for leaving the UK has dropped with 53 per cent backing the status quo and 28 per cent in favour of an independent Scotland.
But SNP strategists are confident that the polls will narrow as they lay out their plans for how an independent Scotland would look. They also expect extending the referendum to 16 and 17-year-olds will increase their support.
"The game has changed considerably in the past couple of weeks," the SNP's deputy leaders Nicola Sturgeon said yesterday. "The good thing about getting the process issues out of the way is that we can get on to that substantive debate about why Scotland would be better as an independent country."
The former Chancellor Alistair Darling, who is leading the cross-party Better Together campaign, said he was pleased the referendum agreement had been made.
"The key thing at stake in these negotiations was to get the single question," he told the Sunday Politics programme. "I would have preferred to have had this referendum in the autumn of 2013 because frankly a two-year election campaign is going to try the patience of the public, never mind the politicians and those who write about it."
The Liberal Democrat Scottish Secretary, Michael Moore, said the process would be "legal, fair and decisive".
"I think it's a good agreement," he said. "I believe it will now allow us to put up in lights the big issues about the big debate... on what is best for Scotland.
"I believe that when we look at the economy, at defence, at our place in the world, on all these big issues people across Scotland will continue to support Scotland being in the United Kingdom.
Independence is about Scotland leaving the UK, becoming a separate state, taking on all the burdens and risks that go with that and losing the benefits and opportunities that we have as part of the UK."