Henry Paulson, the outgoing US Treasury Secretary, said the US Government had to battle the financial crisis without the tools needed to do the job effectively.

Mr Paulson also said any future regulatory overhaul needed to ensure that financial system infrastructure could allow for the failure of large institutions.

In one of his last interviews before leaving office with the Financial Times, Mr Paulson said, “We’ve done all this without all of the authorities that a major nation like the US needs.”

He said that even after Congress in October approved the $700 billion troubled asset relief programme, the US still lacked tools, such as an adequate special bankruptcy regime for non-bank financial firms.

“We’re dealing with something that is really historic and we haven’t had a playbook,” he said.

“The reason it has been difficult is first of all, these excesses have been building up for many, many years. Secondly, we had a hopelessly outdated global architecture and regulatory authorities...in the US,” he was quoted as saying.

Mr Paulson said any regulatory overhaul should emphasise “better and more effective” regulation and needed to make sure that infrastructures and powers were robust enough to allow large institutions to fail.

“The organisations (financial firms) cannot be too big or too interconnected to fail,” he said.

Mr Paulson said he was surprised by the ferocity of the crisis but believed he grasped from August how severe it was as problems at Fannie Mae and Freddie Mac, the home loan funding companies, threatened to coalesce with a dangerous September results season for financial institutions.

“If you asked me six months ago... if I was surprised by the magnitude of the challenge, the answer is ’yes’,” he said.

“But we have been for some time in the frustrating situation of understanding much more than the public or even the Congress understood in terms of the magnitude of what we are facing.”

Asked what the past year has been like personally, he said: “It has been unusually intense.” He said the US Treasury had been going “all out” since July.

Mr Paulson praised his successors, saying: “They have got a great team and they don’t need advice. I really believe that.”

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