Philippa Harrison, managing director of Little Brown UK, which bought the memoirs, said they were "full of revelations" and likely to embarrass a number of people.
Fred Newman, editor of Publishing News, said he understood Little Brown had won the auction with a bid of about pounds 450,000, and he estimated that worldwide book rights alone might make pounds 1m.
Ms Harrison said: "Nick Leeson's manuscript about his last two years is the most compulsively readable story I've seen for many years. The son of a plasterer who ... got involved in a greater gambling binge than any fiction writer could imagine in their wildest dreams."
Ms Harrison said Mr Leeson named names in the book, which is being written in collaboration with a journalist and former banker, Edward Whitley, and is about half-finished.
"It's the most fast-reading, exciting story that you could imagine, and it's full of revelations. It hasn't been read by lawyers yet," she said, speaking at the Frankfurt Book Fair, just miles from the jail where Mr Leeson, 28, is being held pending extradition to Singapore.Reuse content