Two British graduates are on their way back to Britain after being at the heart of a pro-Tibetan protest yesterday that caused deep embarrassment to China as it prepared for the opening of the Olympic Games.

Iain Thom, 24, from Edinburgh, and Lucy Fairbrother, 23, a graduate of Bristol University and the daughter of a former senior bursar at Trinity College, Cambridge, were arrested along with Phill Bartell, 34, from New Jersey, and Tirian Mink, 32, from Portland, Oregon. The Xinhua news agency said that the visas of all four had been revoked and that they would be deported.

In an intriguing twist last night, Ms Fairbrother’s family claimed that their daughter’s online account of a trip to Tibet a few years ago had been altered since her arrest, to become more sympathetic towards the Chinese Government.

During the protest yesterday, Mr Thom and Mr Bartell climbed halfway up two 120ft pylons as dawn broke over the Bird’s Nest stadium that will host the opening ceremony tomorrow.

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They unfurled Tibetan flags and two 140 sq ft banners, one of which read, “One World, One Dream, Free Tibet” — mimicking the “One World, One Dream” official Games slogan. Another called for a “Free Tibet” in English and Chinese.

The two lighting poles are just outside the high-security zone around the stadium. Although the protesters did not have to climb a fence or negotiate the airport-style security gates while carrying ropes and banners, the entire zone is patrolled by police and military personnel through the night.

The role of Ms Fairbrother and Mr Mink was to ensure that the climbers’ equipment was working safely and to protect them from members of the public who might try to intervene.

Footage of the protest appeared to have been taken at some distance from the climbers and their supporters, but there were no reports of any further arrests.

The Chinese Government has deployed 110,000 security personnel across the capital, including 34,000 People’s Liberation Army troops. It has also installed tens of thousands of surveillance cameras in what has been described as the most sophisticated security system for the Olympics.

Organisers of the Students for a Free Tibet group said that the climbers had remained in position for at least an hour after beginning their ascent at about 5.45am.

Lhadon Tethong, executive director of the group, told The Times: “It took [the security forces] at least half an hour to figure out what was going on. Then they used fire trucks and ladders. The climbers came down peacefully and agreeably and met the security.”

Four hours after the protest, the organisation sent to journalists in Beijing an e-mail trumpeting the action, as well as a press release containing biographical details of the demonstrators. It also sent out an audio file of Mr Thom speaking from his mobile phone while 60ft up the pylon.