Scottish Government's Finance Secretary says an oil rich, independent Scotland would be the world's sixth wealthiest country.

The claim follows the publication last September of the 'Official History of North Sea Oil and Gas' by leading oil economist Professor Alex Kemp.

The 14,000 page report, which was commissioned by UK Prime Minister Tony Blair in 1999, says there was evidence that UK governments downplayed the benefits of oil to Scotland's economy to try and avoid encouraging the campaign for independence.

Professor Kemp's report echoed the 1974 McCrone report into the viability of an independent Scotland, which was kept secret for almost 30 years by successive UK governments.

The McCrone report, which came to light in 2005 under the Freedom of Information Act 2000, stated that North sea oil revenue could have made an independent Scotland as prosperous as Switzerland.

Speaking at the Scottish National Party (SNP) conference in October, Scottish Energy Minister Fergus Ewing said North Sea oil and gas would be a key element in the forthcoming referendum on independence.

Finance Secretary John Swinney also told party members: "The figures show that with a geographical share of our offshore resources, Scotland would be the sixth-wealthiest country in the world - 10 places ahead of the UK at 16th."

It is estimated that around 90% of the UK's oil and gas reserves lay within Scottish waters.

The Scottish Government plans to hold a referendum on the issue of independence from the United Kingdom in either 2014 or 2015.