The campaign to keep Scotland in the United Kingdom has officially got under way with a warning from former chancellor Alistair Darling that voting to end the Union will be “irrevocable”.
The Labour MP returned to frontline politics to spearhead the drive against Scottish independence.
Mr Darling was joined by Tories and Liberal Democrats, as well as a number of "real people", for the launch of Better Together which aims to make "a positive case for staying together".
With the independence referendum likely in autumn 2014, Mr Darling said it was "make-your-mind-up time" for Scottish voters.
He said: "The choice we make will be irrevocable.
"If we decide to leave the United Kingdom, there is no way back. We can't give our children a one-way ticket to a deeply uncertain future."
The campaign has the backing of Prime Minister David Cameron who said: "Politics is too often about division. But today, three political parties are joining forces to celebrate the United Kingdom and say it is something worth fighting for.
"We all know Scotland can stand on its own two feet. We just believe the UK is special and we would all lose if separation happened. We treasure our United Kingdom and Scotland's place in our family of nations.
"So this week marks a significant step in the debate over Scotland's destiny as it faces the historic choice: a separate Scotland or a United Kingdom?"
According to a poll of those certain to vote, 55% oppose independence and 35% are in favour.
Mr Darling said such figures show why First Minister Alex Salmond wants the referendum to also give voters the option of backing more powers for Holyrood. Mr Salmond has said that if there is "wide support" for this, it would be "fair and democratic" for it to be included in the ballot.
Mr Darling said: "He wants a second question because its increasingly obvious he is afraid of the first.
"He's worried what Scotland will say in response to the fundamental question, which is whether or not to stay part of the UK. I have this growing feeling he is looking at the polling evidence and coming to the view that anything that muddies the waters might help his cause."
He was speaking at the launch of the Better Together campaign in Edinburgh one month after the Yes Scotland campaign was launched to persuade people in Scotland to back independence and where Hollywood stars Alan Cumming and Brian Cox joined forces with Mr Salmond and Scottish Green leader Patrick Harvie.
In contrast, Better Together featured contributions from Scots who Mr Darling said have "little to do with politics but they are absolutely passionate about Scotland's place in the United Kingdom".
Mr Darling added: "This decision is going to be made by Scotland, the vast majority of people who are not involved in day-to-day politics. In fact for many people, politics is a complete turn-off."
Former Scottish Conservative leader Annabel Goldie introduced the "real people" whom she said will help "decide Scotland's future".
The group included a teacher from Inverness, whose partner is training to be an officer in the British Army; a retired soldier; a young farmer; and an Englishman living north of the border who said he was happy to make Scotland his adopted home.
One shipbuilder committed to a No vote said: "We've been together, we've worked together and we've even fought together. And as the slogan says: we'll be better together."
The drive to keep Scotland in the UK will use the latest technology together with traditional door-to-door campaigning, with half a million leaflets being delivered.
Blue State Digital, the media strategy firm which helped bring US President Barack Obama and French President Francois Hollande to power, has been recruited to build a website and oversee the online campaign.
Mr Darling said leading the campaign for the Union was "one of the most important things I have ever done in politics".
He came together with Tories and Lib Dems to "share a common platform on this single issue because along with so many of our fellow Scots, we believe that a better future for ourselves and our children is as a partner in the United Kingdom".
He added: "I believe we can cement Scotland's place in the United Kingdom once and for all and then get on with building the Scotland we want and deserve."
Scottish Liberal Democrat leader Willie Rennie closed the campaign launch by pledging: "We'll take nothing for granted. In the campaign to keep our family together, we will work for every single vote."
While he accepted that Scottish nationalists were "passionate about their cause" of independence, he said: "I am determined that we will lead a campaign that will match them, and more, with our passion."
Mr Salmond hit back at the former chancellor.
"Alistair Darling's use of smoke and mirrors during his speech exposes a campaign mired in negativity. His threadbare case against independence has been exposed by the weakness of his arguments," he said.
While Mr Darling said Better Together will make a positive case for the Union, this had been "exposed as a fraud".
Mr Salmond said: "Alistair Darling's presentation was littered with words such as borders, division and upheaval; expressing arguments better suited to the 18th century than to the 21st."
Mr Cameron and others suggest that more power could be devolved to Scotland if people vote against independence, but Mr Salmond said the former chancellor "said not a single word" about this at the campaign launch.
"That is because, at heart, this is a Tory-led campaign which is intent on conceding nothing to the people of Scotland and hiding behind its refusal to spell out an alternative policy before the referendum.
"Urging people to vote 'No' with only vague Tory promises of something else will only encourage more people to vote Yes to an independent Scotland.
"The 'No' campaign has had its weaknesses exposed, and Alistair Darling is operating as the frontman for a Tory-led campaign of relentless negativity toward Scotland and its prospects."
In contrast, Mr Salmond said: "Yes Scotland will be relentlessly positive as a winning antidote to the depressing negativity of the 'No' campaign."
Scottish Conservative leader Ruth Davidson said: "Better Together is about giving the shipbuilder from Glasgow to the nanny in Inverness a voice in the biggest decision Scotland has faced in 300 years.
"The voices who came through loud and clear from today's launch include the pensioner from Craigneuk and student from Strathpeffer.
"The future of the United Kingdom is about the future aspirations of a majority of ordinary Scots, who want to remain part of one of the most successful economic and political unions in the world.
"This is about more than party politics or government from one election to the next - there is no going back if we decide to separate Scotland from the rest of Britain.
"Alex Salmond wants millions of Scots to choose between being Scottish and British. The vast majority of Scots are happy with being both.
"Scotland is stronger as part of Britain and Better Together is putting forward a positive case as to why as a nation we should continue to be part of the UK family."