An investment banker who broke the City's "code of silence" as a newspaper columnist has blown his cover to publish a full-scale account of life in the Square Mile.

For 22 months, since shortly after its launch, Cityboy has been thelondonpaper's most popular columnist, exposing the foibles, abuses and monstrous egos that drive the world's most dynamic money markets.

This afternoon, he can be named as Geraint Anderson, a 35-year-old Cambridge history graduate who spent almost 12 years in the City and rose to become a joint team leader and star stock analyst at Dresdner Kleinwort. His book Cityboy – Beer and Loathing in the Square Mile is to be published next week.

Anderson described today how he made the decision to go public on December 19 last year when he was sitting on a beach in Goa – with a margarita in one hand and a joint in the other - having just heard about his annual bonus.

"I didn’t know whether I was going to be given half a million or be sacked," he said. "If they had found out about the column I probably would have been sacked. I was told it was the former.

"In fact it was my biggest bonus ever. I breathed a sigh of relief and planned my escape.

"I’d gone into the City in 1996 with the intention of doing only five years but, like the bank robber in the film, I kept doing one last job. I didn’t want to end up like so many people in the City: alcoholic, red-faced, fat and on my second divorce. The City is full of people like that."

Anderson's book is to be serialised in The Times this week. It is, as its blurb promises, a "no holds barred" account, although he covers his tracks carefully with the disclaimer that while the book is true in the sense of being an accurate picture of life in the City, "none of the characters or institutions portrayed are in any way based on real people or banks".

As fans of his columns will know, Anderson is a born story-teller with an eye for a good line. Describing the day when, at his brother's recommendation, he turns up for his first job interview with "Banque Inutile" he begins: "Everybody sells their soul to the devil... I just decided that I'd get a damn good price for mine."

But while he describes the book as semi-fiction, it reads more like a memoir – and it's hard to believe that Steve Jones, as the main protagonist is called, is not closely based on Anderson himself.

He says: "Let's put it this way: most of those things in the book happened; whether they happened to me or to other people I'm not always going to say.

"I went to Latin America. I took a year off before Cambridge and a year off afterwards and I did a masters in revolutions. Steve Jones did all those things as well."

In fact, Anderson says, he was an unlikely Cityboy. His father is the former leftwing Labour MP Donald Anderson (now Lord Anderson of Swansea). He was brought up not just left-wing but religious.

"I'd always had misgivings about the City," he adds. "But they kept on giving me more cash, which makes it a very difficult job to give up - so it's nice now to have something else to do."

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