The formal campaign to keep Scotland in the UK has been launched with a rallying cry for Unionists to put aside their political differences.

Former chancellor Alistair Darling said the Better Together movement gives a voice to the "quiet majority" in the two years before the planned referendum on Scottish independence.

At the launch in Edinburgh, he said voters are being given a historic choice.

"Chairing this campaign is one of the most important things I have ever done in politics," he said.

"The decision we make is the most important we will make in our lifetime.

"Those of us who believe that it is best for Scotland to be part of the UK, from whatever political views, have a duty now to work in harmony to argue for the better, stronger choice.

"This is a campaign that will make sure that the patriotism of the quiet majority to be heard alongside the voices of the committed view.

"We 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."

With an independence referendum likely in 2014, Mr Darling said it was "make-your-mind-up time for us in Scotland". The vote on Scotland's future was not like "voting in a government for a few years", he said. Instead, it was "about making history".

Mr Darling said: "The truth is we can have the best of both worlds: a strong Scottish Parliament and a key role in a strong and secure United Kingdom." It was not that Scotland could not survive as a separate, independent state: "Of course it could. This is about what unites us, not about what divides us."

The vote on independence was a "chance to reaffirm Scottish values and our expression of them in our partnership with our neighbours", the former chancellor said. "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."

Mr Darling's speech was followed by a film showing Scots explaining why they are comfortable being patriotic while keeping the country in the UK. Students, pensioners and workers all gave their views that it can be positive to vote No in the ballot. They described family and historic ties, saying Scotland is stronger as part of a wider Union including England, Wales and Northern Ireland.

The people featured in the clip were called to the stage, to applause from the audience which included politicians from all the main Unionist parties. It was in contrast to the celebrity-endorsed launch of the Yes Scotland campaign which hopes to secure independence in 2014.

Former Scottish Conservative leader Annabel Goldie, introducing the "real people", said: "These are the people who will decide Scotland's future." They included a teacher from Inverness whose partner is training to be an officer in the British Army.

Another speaker, a retired soldier, said the military shows what strength can be gained from remaining in the Union. "In the Army we are very proud to have such wonderful men and women," he said. "They show toughness and determination. They're a wonderful example of British youth. For that reason we should want to stay together as the British Armed Forces, and pull together when the going gets tough."

A young farmer from the Scottish Borders said she is concerned that her region's natural closeness with the North of England will be cut, and an Englishman said he is happy to make Scotland his adopted home.

Miss Goldie was joined on stage by Kezia Dugdale, a Labour MSP, who spoke to shipbuilders committed to a No vote. One 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."

Scottish Liberal Democrat leader Willie Rennie closed the campaign launch with a call to everyone who wishes Scotland to remain in the UK. People should ask themselves every day how they can play a part in beating the "passionate" pro-independence movement, he said. "In this campaign you will hear why we are safer, stronger, better together. You'll hear from the parties here today but, more importantly, you'll hear from individuals from every corner of every community of Scotland.

"We'll take nothing for granted. In the campaign to keep our family together, we will work for every single vote."

Noting the determination of the Yes camp, Mr Rennie said: "They are passionate about their cause and they will work to win, but I am determined that we will lead a campaign that will match them, and more, with our passion."

He concluded by setting a task for pro-UK supporters: "When you wake up each day, I want you to ask what you can do this day to make Scotland stronger in the United Kingdom. "Raise funds, deliver leaflets: there will be plenty of that. Answer phones, tweet, whatever you can do, because you can do it."