If you want to spot if somebody is lying, ask them to draw...

Asking criminals to draw pictures could be a more effective way of establishing whether or not they are lying than a traditional lie detector test, research has found.

Forensic psychologists at the University of Portsmouth discovered that lying is more obvious in a drawing than in a spoken description.

Lead researcher, Professor Aldert Vrij, said: "A drawing creates several unique problems for liars, not least because a request to sketch a drawing comes as a surprise. This means the liar is unprepared and must do it without planning, and research indicates that people lie better when they have had time to plan their deception."

The researchers developed a test to establish how capable people are at lying when drawing. They sent 31 volunteers on a pretend cloak-and-dagger mission in which they had to collect a laptop from a "secret agent" and deliver it to a second agent. They were then asked to visualise how and where they had received the laptop, describe the scenario and to make a detailed drawing of the location.

Half of the volunteers were instructed to lie about where the exchange took place and half were told to tell the truth. Results showed that only 13 per cent of the liars included in their drawing a sketch of the person from whom they received the package, compared with 80 per cent of those telling the truth.

Professor Vrij said: "Staying close to the truth is often considered to be a good strategy for liars and almost all the liars in our experiment chose to describe and sketch a location they knew.

"However, because it was not the location where they met the agent, when they pictured the location in their mind the agent would be absent from this visualisation. The truth-tellers, however, were more likely to picture the agent in their mind when they visualised the location and include him in the picture."

Another indicator as to who was lying was the perspective from which the drawing showed the scene. Eighty per cent of the liars drew the laptop exchange scene from an overhead position while the majority of truth-tellers showed it from a shoulder height position.

Professor Vrij said the overhead position selected by the deceivers was similar to the way people frequently used indirect forms of speech when fabricating a lie.