Cameron planned to use a speech in Scotland to warn that independence could damage Britain's status in Europe, within Nato and put at risk the UK's permanent seat on the United Nations Security Council.
"The fight is now under way for something really precious: the future of our United Kingdom. I am 100 per cent clear that I will fight with everything I have to keep our United Kingdom together," Cameron said. "To me, this is not some issue of policy or strategy or calculation - it matters head, heart and soul. Our shared home is under threat and everyone who cares about it needs to speak out."
Salmond insists that independence would bring greater prosperity, allowing Scotland to better exploit its energy resources.
"We have 25 per cent of Europe's tidal power potential, 25 per cent of its offshore wind potential and 10 per cent of its wave power potential [which is] not bad for a nation with less than 1 per cent of Europe's population," Salmond said.
Cameron insisted Scotland would be safer and richer if it remained a part of the UK. "We're stronger, because together we count for more in the world, with a permanent seat on the United Nations Security Council, real clout in Nato and Europe and unique influence with allies all over the world."
Cameron insists Scotland's five million people would be more prosperous as part of "the seventh-richest economy on the planet and one of the world's biggest trading powers".
His comments came as the latest jobless statistics showed unemployment at a 16-year record of 2.67 million.
Women are the hidden victims of Britain's flatlining economy, losing their jobs at a far faster rate than men, Office for National Statistics figures revealed.
More than 1.1 million women were on the dole in December - a leap of 91,000 in a year and the highest total for 23 years.
The ONS figures showed the total national unemployment rate rising to 8.4 per cent, the highest level in 16 years, with 2.67 million people out of work. The proportion of 16 to 24-year-olds looking for work, including those fully unemployed, hit 22.2 per cent - about 1.04 million.
- Independent, AP