An independent Scotland would face significant risks to its economy from its disproportionately large banking sector, according to a report that draws parallels with Iceland.

If Scotland had been independent during the financial crisis it would have been forced to turn to the International Monetary Fund, according to the specialist magazine the Banker.

An independent Scotland, with responsibility for RBS, HBOS and Clydesdale Bank, would have a banking sector 12 times larger than the size of its economy, the magazine said on Monday in its annual survey of the world's 1,000 biggest banks. "This would be even larger than the 10:1 ratio that proved so ruinous for Iceland and presents a significant risk for the country's economic stability," it added.

Brian Caplen, the Banker's editor, said: "Had it been independent during the financial crisis, there is little doubt that an independent Scotland would have been devastated and forced to turn to the IMF for help.

"The temptation in future under independence would be to give Edinburgh light touch regulation to make it more competitive as a financial centre. This might have serious consequences."

The prospect of an independent government in Edinburgh relying on outside support to prop up its banks, echoes a warning from the Standard & Poor's ratings agency that an independent Scotland would have to turn to the Bank of England and the Treasury to protect its savers. S&P also drew parallels with Iceland, noting that its national bank-deposit scheme was overwhelmed when the country's huge banking sector collapsed.

All three of Iceland's major privately owned commercial banks collapsed durign the financial crisis of 2008-2011. Photograph: Sari Gustafsson / Rex Features

The banker's calculations are based on the assumption that banks currently headquartered in Scotland would remain there in the event of independence. Mark Carney, the governor of the Bank of England, told MPs in March there was "a distinct possibility" that RBS could move to London.

The pro-independence campaign believes it can create a currency union with the rest of the UK that would preserve the Bank of England as lender of last resort. But the Conservatives, Labour and the Liberal Democrats insist in official statements that an independent Scotland would not be allowed to keep the pound.

Responding to the Banker's report, a Scottish government spokesman said: "These figures are outdated and do not reflect the reality of Scotland's financial sector. Financial services accounts for a lower share of our overall economy at around 7% than they do for the UK as a whole.

"The figures quoted in this report artificially inflate Scotland's financial assets by assigning investment banking activity which takes place almost exclusively in London to Scotland, and by failing to take account of both the recent reforms to the financial services sector and the deleveraging of institutions following the UK financial crisis."

He added: "Independence would create the opportunity for Scotland to pursue a more productive, resilient and fairer economic model that delivered long-term sustainability and economic opportunity for all."

The warning on independence featured in the Banker's annual survey of the world's biggest banks, which lays bare how far British banks have fallen down the rankings since the global financial crisis. HSBC, the only British bank left in the global top 10, slipped to 5th place from 4th in 2013. RBS, on paper the world's third most-profitable bank in 2008, has dropped out of the top 10 entirely.

While British banks are shrinking in profitability, China is soaring ahead and now accounts for nearly one-third of all banking profits. The two most profitable banks in the world are Chinese: ISBC and China Construction Bank are more profitable than JP Morgan and Bank of America, in third and fourth place respectively.