Are you nasty enough to succeed?

You want to get on, you've got what it takes. So how come your equally - nay, less talented - colleague gets promoted to be your boss? Mean thoughts intrude: is it because of they wear the right clothes/flirt with the boss/drink with the in-crowd after work? It would be nice to think that the most able person gets the breaks, but sometimes there are other agendas operating. What are the factors which decide how someone is promoted?

A friend of mine has a theory that mediocrity is the coveted X factor which ensures success. He works in a national communications organisation and many happy hours are spent spotting who will be next in line for promotion. "They are mild and mediocre, the type not to be a threat to the boss," he says.

Being promoted beyond your competence is so widely recognised by human resources experts that it even has its own term, the Peter Principle. "It's uncomfortable to feel challenged by someone who is perceived to be more talented," says occupational psychologist David Wigfield, "and unfortunately this tends to be more acute at the top of an organisation."

The fact is that recruitment decisions are rarely based on rational factors alone. "There is evidence to show that we recruit or promote people who have the right smell or because they trigger a positive memory from early childhood," says Ben Williams, Edinburgh-based corporate chartered psychologist. "If someone makes the right tribal noises, belongs to the same golf club or trade union, it's natural to want them on your team. I once knew an industrial nurse who wanted to recruit someone from her old regiment. 'I know she'll take orders from me and recognise me as her senior', she said."

Termed the "confidence model" (because shared values inspire confidence), it can also work to your advantage. My break in journalism came over lunch with the then editor of Parents magazine - I was all ready to play down my role as an active birth campaigner, but it turned out to be just the kind of thing to make me employable.

But if employers always promote those from their own in-group, what happens to people who belong to a different race, class or gender? Many find themselves facing an invisible barrier against promotion - the glass ceiling. A good example is how few NHS merit awards (hefty bonus payments) are given to senior doctors who are either female or from ethnic minorities.

Although most bosses probably look for a mix of eligibility (qualifications) and suitability (the face fits), the problems start when the balance is skewed. Knee-jerk tribalism is not only unfair if you are excluded, it can also produce a lack-lustre team, according to David Wigfield. "It's terribly easy to select people in your own image," he says, "but research suggests that highly productive teams are those which combine a mix of talents, personalities and cultural backgrounds. With the right leadership, such a team can be dynamite because different people bring unique strengths. When team members are too samey, the results tend to be rather mediocre."

Perhaps mediocre people are easier to manipulate. Carla works in an office where a new employee was given a post over the heads of two skilled, eligible women. "He's proving to be incompetent and we all have to work extra hard to pick up the pieces. We suspect that he was promoted because he is a pussy-cat and doesn't answer back to our female boss."

It's not all one way. Workplace dynamics can be as enmeshing as the most intimate of relationships and it's easy to get sucked in. Jim had a subterranean struggle when he tried to leave personnel for the creative hub of production. "My boss in personnel said she was in my corner," says Jim, "but at the same time she would use an accusing tone of voice as if there was something wrong with my ambition to move into production. She gave me slightly off advice which hampered me. Looking back, I think my moving on made her feel insecure. I didn't realise until it was nearly too late how her anxieties were holding me back."

Some of these subtle reasons why people may or may not get promoted are difficult to prove. Workplaces seethe with rumours in the absence of hard evidence: did they get the job because they wear the right clothes/behave like a bully/belong to the boss's club? Ben Williams warns that this kind of veiled culture can be destructive to employees. "Word gets out. Someone asks, 'is there a problem with so and so?'. 'I'd rather not say,' says another. 'Enough said, old chap,' his colleague replies. And before you know it, what began as a minor misdemeanour like parking in the director's car space has turned into a major scandal," he says.

If minor transgressions can offend the work culture, then the message is clear: don't rock the boat if you want to get on. Everyone I interviewed about their workplace insisted on complete anonymity - no one wanted to be seen as critical or bolshie. This can sometimes leaves employees with stark choices between their own integrity and their promotion. When Dr Stephen Bolsin wrote to his boss about the high death rate of babies having heart operations in Bristol, he was warned that future letters of this sort would jeapordise his career.

"By raising the alarm, I was seen as the problem," he has said. "I was shunned, devalued and criticised. I was not invited to meetings and my work as a consultant was cut back to one day a week. Professional loyalty appeared to count more than dying babies." Ben Williams calls this inverted promotion, when someone's career is actively blocked and sidelined.

Stephen Bolsin suspects that he came up against a covert in-crowd culture, in this case freemasonry. The role of freemasonry is to be investigated by the independent public inquiry which opens in Bristol this week.

Sometimes it takes things going badly wrong to make people wake up and change the system. Over the years the police have also been charged with being susceptible to vested interests, like masonry. But now police forces employ occupational psychologists like David Wigfield, who works for Sussex Police, to ensure that promotions are made as fairly and as objectively as possible.

"Increasingly the police and other public sector organisations are becoming aware of their need to be accountable to the public," says David Wigfield. He has helped institute a grieviance procedure so that the reasons for promotion will stand up to a third party investigation. "The key is a promotion system that is transparent and open to scrutiny," he says.

Finally, if your workplace hasn't yet caught up with the current trend to promote for the greater good (and not to prop up the boss's wobbly psyche) then Ben Williams has some advice. "Don't be tempted to kow-tow. Carry on being yourself because that is the most powerful way to change a culture."

Brave words. But will it help your promotion? Or it is a case of waiting until the shady networks have been called to account before you can take your rightful place in the sun?