Liar, liar, pants on fire

...Or not, as the case may be. The trick is to spot the lie in the making from the battery of ticks, tugs and twitches with which we betray our deceit. So how do you tell a porky from the gospel?

Wouldn't it be great to know when someone was lying to you? Almost as good, in fact, as being able to lie to other people without their knowing. The skills involved are much the same. Presumably that has not escaped the attention of managers who are flocking to learn how to detect lying, fraud and general dishonesty in the workforce.

The early detection of lies - or, to be more precise, the promise that lies can be detected - is now big business for those offering everything from training to PC software guaranteed to unmask the dishonest by the tremor in their voice, as they assure you that you really have won a valuable holiday.

At a conference in Westminster this week, delegates have been hearing how to detect potential corporate fraudsters in the Nick Leeson mould by "psychometric testing and psychometric profiling" of both fraudsters and victims. It has been suggested that, among other things, they will be looking at that video in which President Clinton denies having sex with "that woman".

Clinton's demeanour is typical of what we all take to be the characteristic behaviour of liars: the lack of eye-contact, the blushing, the perspiration, the wavering voice and the endless fidgeting with tie and cuffs and ball- point.

If only it were that easy. Psychologists agree that we all believe we can detect liars, and we are usually wrong. The researcher G Kohnken, in 1990, wrote: "When we are asked to estimate our ability to detect deceptions, we remember only the gross and awkward lies which were easily detected.

"Most of the skilful, clever, successful lies, on the other hand, are never noticed. In fact, this is the very reason why they were successful." In other words, because we think it's easy to spot a liar, we are highly susceptible to those who do it skilfully.

Those non-verbal giveaways are easily controlled by serious liars. As any parent knows, it does not take long for a child to spot the kind of behaviour that adults associate with honesty: "No," they will say, eyes staring tearfully into yours, "I didn't thump the baby."

However, the liars aren't having it all their own way. Research at Hertfordshire University has shown that while the obvious indicators can be suppressed, certain "micro-expressions" are still be there: momentary hesitations, uncomfortable expressions, flickers of the mouth or eyebrows as the pressure of control seeks an outlet.

The problem is that we don't see them. But if you make a special video, taking a picture once every second, and then play it back at normal speed, the odd expressions and unnatural head movements jump out.

A boon, this, to the university's corporate clients, desperate to screen out a liar at the interview stage rather than waiting until he is made finance director. But for the rest of us it is of limited practical use. "Yes," you may say, "I am very interested in that pair of cut-price hi- fi speakers that you happen to have in your white van. But would you like to say it again for the camera?"

Often it makes more sense to judge people by what they say, rather than how they behave. Dr Richard Wiseman, at Hertfordshire University, did an experiment in which people were shown a television interview, a radio interview and a print interview specially staged with Sir Robin Day, and asked to say when he was lying. The guesses for print and radio were much more accurate than for television, where people took Day's relaxed professionalism for honesty: a useful pointer for those planning a broadcasting career.

Recruitment interviewers know that evasion, and skimpy information, are common signs that something is amiss, as are hesitation and clumsy attempts to change the subject. But, in other circumstances, quite different rules apply.

When caught out, liars will often give too much information, telling a story that is too structured, polished and complete. If you find someone wandering around in your office, don't be surprised when they start telling you that they have been sent by head office to do a survey of the positioning of water coolers for health and safety reasons. They've probably come to steal the photocopier.

An undetectable, unarguable, physiological method of lie-detection remains the corporate Holy Grail. But the polygraph, the "lie detector", is probably not the answer. There are several books explaining how to beat it, one of which is by Doug Williams, a former police officer, who points out that his aim is to help honest people to defend themselves.

To publicise his How To Sting the Polygraph, he showed honest truth-tellers being fingered as liars in three separate tests. Then he told the machine a series of whoppers, starting with a false name, only for the polygrapher to declare him "the most honest person I have ever tested." Or so he says...

More tempting is the Truth Tester, a piece of $200 Israeli software that analyses imperceptible quaverings in the spoken voice, allowing users to test people's veracity over the telephone. Political correspondents might think that a valuable investment.

The truth is that honesty is overvalued. Researchers at the University of South Carolina showed that people lied on average 200 times a day, or about every eight minutes. True, most of these lies were along the lines of "How nice to see you" and "Sorry to bother you", but they were still falsehoods. However, as Professor Gerald Jellison of the university put it, "Society would be terrible if people started telling the truth. Anyone who did would be a subversive."

It seems unlikely to happen. Lying is as old as mankind. Everyone knows that in Eden the snake lied to Eve, landing her and Adam in a great deal of trouble. Which only goes to show the danger of taking an unblinking gaze as an indicator of honesty.

Sometimes it just means a lack of eyelids.