Dame Marjorie said, however, that the former US Federal Reserve Chairman is proving to be “a diligent author” who will definitely help his publisher to make a return on the $8.5 million (£4.5 million) that it spent to secure the rights to produce his memoir.

Dame Marjorie had to personally sign off on the advance — and inform the company’s board — because it was so large.

Mr Greenspan, who met Dame Marjorie for dinner after Penguin signed him up, has agreed to produce the first and last drafts of the eagerly awaited book. The former Fed chief is apparently “working on the text every day”.

Mr Greenspan has hired Peter Petre, a senior editor at Fortune magazine, to help to redraft and ghost-write his text. It is understood that Mr Greenspan held interviews for ghost writers to prove their credentials.

Pearson’s decision to pay for Mr Greenspan’s memoir earlier this year flew in the face of Penguin’s new strategy of concentrating on cheaper, first-time authors. However, Dame Marjorie, speaking about the fee for the first time, said that she expected the tome to be a long-term seller. “It will run and run, because economic students will buy it for years,” she said.

Mr Greenspan was Chairman of the Federal Reserve, the US central bank, from 1987 until 2006. He won praise for his handling of the 1987 economic crash, which he helped to staunch with the terse statement that “the Fed stands ready to provide all necessary liquidity”.

Pearson said that the book is due to appear in the autumn of next year.

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