One of the world's best-known billionaires has waded into the Scottish independence debate, as the world's 42nd largest economy suddenly shifts to the top of the business world's agenda.

George Soros, who famously made his fortune betting against sterling, wrote in the Financial Times that this was the "worst possible time" for Scotland to think about leaving the Union. He argued that the impact on the U.K.'s international standing would be huge, and called for "increased unity."