We all like to think we’re unique; intriguing, one-off blends of nature, nurture and our own quirky characteristics. But, according to an increasingly influential band of “personality measurers” in industry, recruitment and even counselling, we are not as singular or original as we imagine. This, they claim, is because every human personality can be categorised (“typed”), according to the answers given to a series of questions.

So when you are applying for a job or being assessed at work, you may unwittingly give a “false” impression - unless you spotted the hidden agenda behind the questions and adjusted your answers accordingly.

Personality questions - or “psychometric tests” as they are known in the human resources world - arrived here from the US in the Eighties and are now big business. According to Saville and Holdsworth, the UK’s biggest publisher and trainer in the field, 50 per cent of “large” companies now use occupational personality questionnaires (OPQs) to recruit and assess staff. Saville and Holdsworth’s clients include Safeway, Barclays, British Nuclear Fuels, Virgin Trains, local education authorities, health service departments and London boroughs.

The company is understandably touchy about any suggestion that their tests might be unreliable. “Of course there’s a risk that some people won’t answer honestly,” says a spokesman. “Fake ability is a complex area, but I don’t think many people would want to tweak themselves for a job they’re not suited for. In any case, there are no absolute rights and wrongs; it’s just that some types of personality are better fitted to certain sorts of job.”

As personnel advisor to Surrey education department, Mary Sharp uses Saville and Holdsworth’s OPQs to help school governors select new head-teachers. “It is not used to make judgments, and there is no ‘perfect profile’ for a headteacher,” she insists. “It’s just a useful information gathering device. ”

Another system, the much gentler Myers Briggs Type Indicator, is favoured for career development, team-building and “individual self-knowledge”. Based on Carl Jung’s work on “types”, the MBTI was devised 50 years ago by the American psychologist Isabel Myers, based on research she had conducted with her mother, Katherine Biggs.

According to the Myers Briggs theory, every personality falls on one side of four dividing lines: extroversion (E) versus introversion (I); sensing (S) versus intuition (N); thinking (T) versus feeling (F); and judging (J) versus perceiving (P). How far you lean in each direction depends on the consistency of your answers to 88 multiple-choice questions (see the sample below).

The four preferences combine to reveal one of 16 personality “types”. For example, there are the INFPs, who are introverted, intuitive, feeling and perceiving, as opposed to the ESTJs, who are extroverted, sensing, thinking and judging. However, a Myers Briggs label indicates only preferences. “Feeling” people also think, and “perceiving” people also judge.

When Myers Briggs is used for team-building, each person completes a question on which they are debriefed, then the whole team meets to explore ways in which their styles can be used to complement each other. So the introvert who thinks the extrovert talks without thinking, and the extrovert who thinks the introvert has nothing to say, both discover (in theory) that the other is not the idiot they thought they were, but just a different psychological type.

The system is being used by British Airways to foster camaraderie within its flight crews, and in an educational pilot project in Hackney, east London, to help unemployed 18 to 22-year-olds to find suitable jobs.

Nadine White, who teaches English, drama and art at an Oxfordshire secondary school, first encountered Myers Briggs while teaching in her native America in the Seventies. She now uses it in her part-time role as an advisory teacher and educational consultant. She has run MBTI workshops for the senior management team of her own school, for Henley Further Education College, and Oxford education authority.

“For me, discovering Myers Briggs was like a light going on,” she says. “I find it very useful because it’s a value-free indicator. No judgments are made - it simply shows how people prefer to go about doing things.”

Oxford education authority’s professional development officer, Rosemary Napper, invited Nadine White to run a workshop for 55 community education workers. There were going to be redundancies following a major departmental reorganisation, and she felt MBTI might help staff identify their strengths. “I’m not sure about its long-term usefulness for such a big group,” she admits. “But it was very enjoyable at the time. People love doing the questionnaires because they’re fun, like a Cosmo quiz.”

Steve Jorgensen, headteacher of Prescot Primary in Merseyside and a former secretary of the National Association of Head Teachers, is full of praise for a third personality typing system, the Enneagram. This is an ancient spiritual and psychological diagram of the human personality, said to have its origins in Sufi mystical teachings.

Favoured by the Jesuits and other religious groups, the Enneagram identifies you as one of nine personality types: the perfectionist; the giver; the performer; the romantic; the observer, the questioner; the epicure; the boss; or the mediator. These are represented as points on a circle, each connected by arrows to two other types that the personality veers towards in times of stress or security.

Steve Jorgensen attended his first workshop out of curiosity six years ago and was amazed to discover how perfectly he fitted the performer type. “The biggest shock was discovering that everyone else didn’t think the same way I did, ” he says. “I’m extremely competitive, ambitious and task-orientated, and when I became a headteacher at 30 I assumed I’d beaten everyone else to it. It never occurred to me that some people might not want to be heads.”

He believes that this realisation has made him a better manager. “The Enneagram defines your natural reactions in different situations and also teaches you that these are not the only reactions. So now, when I consider someone is out of order, I’ll step back and think about who they are.

“I don’t consciously ‘type’ people, but I’m aware of the reactions of different personalities. For example, if you have something unpleasant to say to a Type Five (the observer), they’ll be stunned and switch off, so it’s better to say you’ll see them again tomorrow. But if you say the same thing to a Type One (the perfectionist), they’ll come straight back at you.”

Despite his belief in the system, Mr Jorgensen tends not to plug it in his staffroom. “I’ve talked to colleagues about it, but that kind of thing doesn’t really run up here. In Liverpool, if you have a problem, you go for a pint. ”

For OPQs: Saville and Holdsworth, 3 AC court, High St, Thames Ditton, Surrey KT7 0SR. Tel 0181 398 417. For Myers Briggs Type Indicators: Oxford Psychologists Press, Lambourne House, 311-321 Banbury Road, Oxford OX2 7JH. Tel: 01865 510203.For Enneagram workshops in Britain: Karen Webb, Enneagram Studies in the Oral Tradition, 66 Cowleigh Bank, Malvern, Worcestershire WR14 1PH. Tel: 01684 561258. Retreat houses running MBTI and Enneagram workshops are listed in ‘The Good Retreat Guide’ by Stafford Whiteaker, Pounds 12.99 from Rider Books