By Daniel Hunter

In what was his final Mansion House speech, Lord Turner, the head of the Financial Services Authority, has suggested that it may be time for more unconventional policies to revive Britain's stagnant economy.

Lord Turner, who is seen as a leading candidate to take over as the next governor of the Bank of England, said reducing private, business and government debt following the financial crisis could impact economic growth for many years.

Lord Turner also questioned the continuing effectiveness of Bank of England stimulus.

The financial crisis of 2008 was "not a bolt from the blue," he said.

"It arose from poor supervision, from bad rules and structures, from dangerous cultures - and the errors were made by regulators, economists, central bankers and public policy makers, as well as bankers themselves," he said.

"There are increasing signs that many banking industry leaders recognise the need for major change". Some observers have questioned whether the industry has learned lessons from the crisis, arguing that too many bankers have returned to business as usual.

"If we do not carefully design policy in response, the deflationary impact on economic growth could extend for many years ahead," he said.

Lord Turner also questioned how effective the Bank's stimulus measures have been.

"QE alone may be subject to declining marginal impact," he said.

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