THE ancient and blood-curdling roots of the spin doctor phenomenon have been revealed.

An investigation, using the latest computer-enhanced imaging techniques, has unlocked the secret censorship ritual of the ancient Mayan civilisation in its quest to show that the sword is mightier than the pen.

The study of murals painted in Mayan buildings has revealed details of how official scribes of kings who had been conquered by rivals had their fingers broken and were then executed in public rituals.

Professor Kevin Johnston, assistant professor of anthropology at Ohio State University, made the discovery while making a new investigation into Mayan art after he saw photographs of murals in an issue of National Geographic.

He said: ''By breaking the fingers of scribes, what they were really doing was muting the ability of scribes to write politically powerful texts for their defeated king.

''Texts were a way that kings asserted and displayed power, and so the scribes who produced them were targeted during warfare for destruction. The captors emphasised, through finger mutilation, the destruction of their rivals' ability to produce politically persuasive texts.''

These texts would extol the virtues of the king and promise material rewards to those who supported him. Texts also describe the consequences for those who were insubordinate.

Professor Johnston believes the scribes' torture and execution showed the importance they played in Mayan society, which reached its height from about AD 600 to 900 and occupied parts of present-day southern Mexico, northern Guatemala, Belize and western Honduras.

One mural, found in the Maya site of Bonampak, in the Chiapas state of southern Mexico, shows nine captives crouched at the feet of the victorious king and his supporters. In the mural, red paint signifies blood dripping from the broken fingers of some captives.

The murals depicted some of the scribes having their fingers twisted and fingernails removed.

Computer-enhanced images also revealed one captive holding up a quill pen, as if recording his capture and execution.

Professor Johnston found five other works of Mayan art that support his thesis that scribes were tortured and killed for their politically powerful role supporting conquered kings.

''We've long known that these people in the mural were captives, but no-one had thought much about their status - who they were in Maya society. The new photographs clearly suggest that these men were scribes.''

Kings had to use persuasion as much as direct power to exercise control over their kingdoms.

Jack Irvine, executive chairman of Media House, a leading public relations firm based in Glasgow, said: ''In a sense, nothing has changed. The first thing that happens when a company is taken over is they get rid of the PR people. There are parallels.

''It was actually a very practical measure, although if they were going to kill them anyway, it was a bit evil as well.''