Everybody lies at some point; politicians seem to lie most of the time. The question is, can you spot a liar? Are there any tell-tale signs to alert you that what you are hearing is nothing but the truth? Tom Nevin has been investigating.

When the Premier of South Africa's Mpumalanga province, Mdaweni Mahlangu, said recently that it is okay for politicians to lie, the resulting public outcry was caused not so much by his statement's factual correctness but by its political incorrectness.

The matter has now officially been put to rest and we'll never find out if he knew something we do not but he was not really letting that much of a cat out of the bag. We all know that politicians' treatment of the truth can be pretty casual at times and that they will bend the facts to make political points. Catching them at it, however, is something else entirely.

Can you always tell just by watching someone if they're lying? If you say you can the chances are, according to the experts, that you may be straying from the truth yourself. Researchers say that just about everybody tells lies. Studies show that people can detect other people's lies just a little over half the time, slightly better than even money. And some experts suggest people trained in police work or psychology push the score up considerably.

Researcher Paul Ekman is a psychologist at the University of California and his studies propose that around 90% of liars give themselves away by making 35 different errors such as involuntary facial movements, voice tics and nervous gestures. At the same time, Ekman's team found that professionals such as lawyers, and law enforcement officers (principally CIA agents) could spot the liars 73% of the time. A group of clinical psychologists scored 68% while officers from the LA sheriff's department scored 67%.

Professor Bella DePaula, however, doesn't agree. The University of Virginia psychology professor does not think that Ekman's results necessarily mean that interrogators will consistently score over the odds. DePaula, who is doing her own research into lying, found that the old cops didn't score any higher than the rookies, "They just thought they did," she said.

Ekman concedes that most police believe between 70-80% of people are lying and rely to a great extent on their street education, which could mean they over-estimate their abilities. He believes, however, that lie detection can be taught and he holds seminars for judges, police officers and other seekers after the truth.

Clues include a 'lack of coherence' in answers, 'words that don't fit the facial expression' and 'gestures that don't fit the voice'. Another researcher says you have to watch and listen carefully to a subject "There are a cluster of things that a person does before and when he lies. There is no Pinocchio response."

Researchers agree that it is not easy to assemble foolproof tests, or even those that provide constant high scores. DePaula for one doubts that lie detection can be taught as a skill; she does concede that as a practice it does improve with familiarity, particularly among women.

DePaula stresses the importance of the 'context'. If police officers are "good at detecting the lies they're supposed to detect, what does it matter if they go home and believe their teenage son when he says he's going to the library on Friday night?"