Lawmakers from Britain's three main political parties launched a campaign against Scottish independence on Monday, insisting that Scotland benefits from the United Kingdom's "unique influence".
Alex Salmond, Scotland's First Minister and leader of the pro-independence Scottish National Party (SNP), plans to hold a referendum in autumn 2014 on severing the more than 300-year-old union and launched its campaign last month.
But as the "Better Together" campaign launched in Edinburgh, British Prime Minister David Cameron said a united Britain was "something worth fighting for".
"We all know Scotland can stand on its own two feet," said Cameron, whose Conservative party backs the union along with its junior coalition partners the Liberal Democrats and the opposition Labour party.
"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."
Pro-union campaign leader Alistair Darling said Scotland currently enjoyed "the best of both worlds" through the devolved powers of its parliament at Holyrood and its role in British government.
"The United Kingdom is a country with unique influence -- in the EU, in the Commonwealth and in the G20 group of the world's largest economies," the former finance minister said as he launched the campaign in the Scottish capital.
"Why would we want to give away this deep influence?"
Speaking at Edinburgh's Napier University, Darling said that Scotland has "real clout" in the UN Security Council, the European Union, the International Monetary Fund and NATO as part of Britain.
Darling, the Labour Member of Parliament for Edinburgh South West who was Chancellor of the Exchequer from 2007 to 2010, said the decision would be "the most important we will make in our lifetime".
He added that independence would be an "inadequate response" to Britain's economic problems.
"Times are really tough at home and really uncertain, especially in Europe, where all the problems of a currency union are laid bare," he said.
Responding to the speech, Salmond branded the pro-union case as "threadbare".
"The anti-independence campaign's claim to be making a positive case has been exposed as a fraud," he said.
"Alistair Darling's presentation was littered with words such as âborders', âdivision' and âupheaval', expressing arguments better suited to the 18th century than to the 21st."
Salmond, who has pushed for a referendum since his party won a majority in Holyrood in 2010, says Scotland should be able to run its own foreign, economic and defence policies.
The Scottish government currently has powers over some policy areas such as health and education, but control of defence, energy and foreign affairs remains in the hands of the British government.