GCHQ analysts believe the decision was deliberately calculated by the Beijing leadership to provide an excuse to stamp out the simmering unrest in the region, which is already attracting unwelcome world attention in the run-up to the Olympic Games this summer.

For weeks there has been growing resentment in Lhasa, Tibet's capital, against minor actions taken by the Chinese authorities.

Increasingly, monks have led acts of civil disobedience, demanding the right to perform traditional incense burning rituals. With their demands go cries for the return of the Dalai Lama, the 14th to hold the high spiritual office.

Committed to teaching the tenets of his moral authority - peace and compassion - the Dalai Lama was 14 when the PLA invaded Tibet in 1950 and he was forced to flee to India from where he has run a relentless campaign against the harshness of Chinese rule.

But critics have objected to his attraction to film stars. Newspaper magnate Rupert Murdoch has called him: "A very political monk in Gucci shoes."

Discovering that his supporters inside Tibet and China would become even more active in the months approaching the Olympic Games this summer, British intelligence officers in Beijing learned the ruling regime would seek an excuse to move and crush the present unrest.

That fear was publicly expressed by the Dalai Lama. GCHQ's satellites, geo-positioned in space, were tasked to closely monitor the situation.

The doughnut-shaped complex, near Cheltenham racecourse, is set in the pleasant Cotswolds in the west of England. Seven thousand employees include the best electronic experts and analysts in the world. Between them they speak more than 150 languages. At their disposal are 10,000 computers, many of which have been specially built for their work.

The images they downloaded from the satellites provided confirmation the Chinese used agent provocateurs to start riots, which gave the PLA the excuse to move on Lhasa to kill and wound over the past week.