The referendum will ask voters whether they want Scotland to remain in the 305-year-old union with England.
Cameron opposes a break-up of the union, arguing that Britain is stronger together, and opinion polls show only between 30 and 40 percent of Scots support independence.
Scotland and England have shared a monarch since 1603 and have been ruled by one single parliament in London since 1707. In 1999, for the first time since then, a devolved Scottish parliament was opened following a referendum.
(Reporting by Maria Golovnina; editing by Stephen Addison)