Most people have encountered a colleague who is manipulative, dishonest or willing to step on others to get ahead. But at what point does fierce ambition cross into something more troubling?

Former London banker and author Geraint Anderson says he knows what that line can look like.

The 53-year-old said a clinical psychologist recently assessed him and suggested he may have developed what was described as “situational psychopathy” during his years working in London’s fiercely competitive financial sector.

“I had to really become a kind of worse version of myself in order to thrive in this environment,” Anderson said.

Anderson spent 12 years working as an analyst in London’s financial district, where he made millions of pounds before leaving the industry ahead of the 2008 financial crisis.

He believes the culture rewarded traits associated with the so-called “dark triad” of personality characteristics, including confidence, manipulation and emotional detachment.

“The City rewards this dark triad behaviour… being uber confident, being able to control and manipulate others, not getting emotionally involved in decisions and being decisive,” he said.

“I adapted myself for the City and started bringing out the kind of worst side of myself.”

What does psychopathy mean?

Psychopathy is not, by itself, a formal clinical diagnosis. The term is generally used to describe a collection of traits associated with antisocial personality disorder, including manipulation, exploitation, a lack of remorse, irresponsibility, unstable relationships and an unwillingness to accept blame.

Anderson’s journey into finance began after he left behind a carefree life in Goa, India, and followed his brother’s advice to apply for a job in the industry.

For the interview, he dramatically changed his appearance, cutting off his ponytail, shaving his beard, removing his earrings and buying a £60 suit.

He initially planned to stay in finance for only a few years. But once he landed an internship, professional success became increasingly important to him.

He viewed his bonuses as a measure of how successful he was and used them to compare himself with employees at other banks.

Anderson believes some of the qualities that helped him climb the corporate ladder overlapped with psychopathic traits.

“I had a degree of fearlessness. I had a bit of — dare I say — glib charm. I wasn’t hugely emotionally affected by things that happened on the trading floor,” he said.

Robert Snowden, a Cardiff University psychologist who has spent around 25 years studying psychopathy and has worked with psychologist Robert Hare, said the condition exists along a spectrum rather than as a simple yes-or-no category.

Hare’s Psychopathy Checklist-Revised contains 20 items, with scores ranging from zero to 40. Snowden said most people score below five, while 25 or higher is generally considered the threshold associated with psychopathy.

Anderson put his own score at around eight or nine.

“Psychopathy is on a dimension that I could place you, I could place myself,” Snowden said.

According to Snowden, the central characteristic is a lack of empathy.

“Most psychopaths never kill anybody. But they may take advantage of other people, exploit other people, not care about other people,” he said.

Some corporate environments may be particularly attractive to people with psychopathic traits, Snowden said, because they can reward emotional detachment, competitiveness and an intense focus on financial gain.

While some of these traits may help people perform well in high-pressure leadership roles, they can also become damaging when leaders become primarily concerned with themselves and their own interests.

Can a workplace bring out psychopathic traits?

Consultant and forensic psychologist Kerry Daynes recently assessed Anderson and concluded that he was not a psychopath.

Instead, she suggested his behaviour could have been an example of “situational psychopathy” — adapting one’s personality and behaviour to succeed in an environment that rewards ruthless ambition.

“You don’t need to be a psychopath to thrive — for a while at least — in a psychopathic culture,” Daynes said.

She said Anderson had managed to amplify some of his darker personality traits to a level that gave him an advantage in his professional environment.

But eventually, the culture he had embraced began to wear him down.

Anderson became increasingly uncomfortable with what he saw as the financial industry’s “greed, reckless risk-taking and rule breaking”.

“I just looked around and thought ‘I’m on the wrong team’… What on Earth are you doing? You are part of the problem,” he said.

He eventually left finance and began writing anonymously as Cityboy for the London Paper, exposing the industry’s culture of lavish spending, drugs, excessive drinking and illicit sex.

His columns were later turned into the book Cityboy, which sold more than 400,000 copies and was translated into six languages.

His latest book examines how adopting psychopathic traits can help people climb the corporate ladder.

Anderson says he is a different person now, describing himself as less pleasant during his corporate years than he is today.

“I’m more able to feel like trying to have integrity and not manipulate and be ruthless,” he said.

Although, with a joke, he acknowledged that his wife might have a different assessment of how completely those darker traits have disappeared.