A Briton and an Australian-Canadian staged the latest challenge to Chinese rule in Tibet this morning, climbing up a huge billboard in front of the headquarters of Chinese Central Television in Beijing and unfurling a huge banner calling for a free Tibet.

Philip Kirk, 24, from Hertfordshire and Nicole Rycroft, 41, a former national rower for Australia, carried out the latest demonstration against Chinese rule of the deeply Buddhist Himalayan region. The move is deeply embarrassing for China with the eyes of the world watching it during the Olympic Games.

The pair climbed scaffolding behind a billboard in front of the newly built headquarters of CCTV, a dramatic structure in the shape of a twisted Z and the largest building in the world after the Pentagon. The pair then rappelled down the front of the hoarding covered with a slogan celebrating the Olympic Games that read “Beijing 2008”.

They were able to unfurl a banner reading “Free Tibet” in both English and in Chinese as well as banned Tibetan Snow Lion flags that Beijing associates with the exiled Dalai Lama and with movements demanding an end to Chinese rule there.

The two climbers, accompanied by three Americans who provided support from the ground, were able to stay on top of the billboard for about 30 minutes, from 5.45 amto 6.20 am before police brought them down, said Lhadon Tethong, head of the Students for a Free Tibet group, which organised the daring demonstration.

She said the group had called from the police van after they were detained to say that they were all well and expected to be swiftly deported as has been the case in three previous protests staged by the group to coincide with the August 8-24 Games.

Ms Tethong told The Times: “The CCTV building represents a mouthpiece of the Chinese government, their propaganda and lies that they spin not just to the world but to the Chinese people themselves.” The activist group has sought to use the Olympic Games to publicise its criticisms of China for alleged repressive rule in Tibet, rights abuses and religious restrictions.

Beijing has been particularly sensitive about the Tibet issue since a bloody riot in Lhasa in which rampaging Tibetans set fire to dozens of buildings and killed about 22 people, most ethnic Han Chinese. The demonstrations spread to many other Tibetan areas, underlining the depth of anti-Chinese feeling and demands for the return of the Dalai Lama, who fled into exile after a failed uprising in 1959.

Ms Tethong said: “The state media in China has been used to misrepresent the Tibetan issue, the demands of the Tibetan people and the nature of their protests. The media have been used to the detriment not just of the Tibetan people and their future but all of China. That is why we have done this.”