'Brand Britain' is worth £1.4tn, but its value is under threat from the prospect of Scottish independence.

That is according to a report by consultancy firm Brand Finance, which assesses the value of nation brands by analysing factors such as GDP projections, quality of life and the quality of the workforce and compiles an index.

Britain came in at fourth on the index, behind Germany in third, China in second and the United States in the top spot.

Scotland is facing a 2014 referendum on independence that would see it break up its historic British union with England and Wales and run itself from Edinburgh as a sovereign state.

"Scottish independence, however noble the motives of its supporters, represents a significant threat to both Scotland and England," said David Haigh, chief executive of Brand Finance.

"The nation brand value built up over centuries and in the last few years so successfully fostered by the government's GREAT Britain campaign would be squandered.

"The combined nation brand values for an independent Scotland and England are likely to be substantially lower than that of a united UK, in the medium term at the very least."

The Scottish National Party (SNP), which secured the referendum, has published its White Paper on how it would break free from Westminster's political control.

It has been criticised for a lack of detail on the mechanics of independence, but the paper pledged to keep the British monarchy, pound sterling as its currency and membership of the European Union.

"We know we have the people, the skills, and resources to make Scotland a more successful country," said Scottish First Minister Alex Salmond at the launch of the white paper.

"Independence will put the people of Scotland in charge of our own destiny."

UK Chancellor George Osborne claimed Scottish families would be significantly worse off if the country split from Britain, with a loss equivalent to £2,000 per household on average.

Osborne was delivering a keynote speech at an Aberdeen oil and gas industry conference to coincide with the launch of a Treasury report, called Scotland Analysis: Macroeconomic and Fiscal Performance.

The 140-page report was the fifth in a series published by the UK government analysing Scotland's place within Britain and the scenarios that might unfold if it left.

It said Scottish GDP would be 4% higher in 30 years if the country remains within the UK because of the lucrative trading relationship between British nations as well as the anticipated growth in economic activity.