http://news.bbc.co.uk/1/hi/uk/7544416.stm
Britons held in Beijing protest
Beijing protester and banner
The protest is thought to have involved members of a student group
Two Britons have been detained in Beijing after a protest about Tibet.
The group Students for a Free Tibet said four activists from the UK and the US were arrested after unfurling banners close to the Olympic stadium.
The UK protesters are Iain Thom and Lucy Fairbrother. The campaign group said Mr Thom, 24, is from Edinburgh and Ms Fairbrother, 23, is from Cambridge.
A spokesman for the Beijing Olympics described the protest as "unacceptable and "illegal".
Students for a Free Tibet named the American protesters on their website as Phill Bartell, 34, from New Jersey and Tirian Mink, 32, from Portland, Oregon. The group added that Lucy Fairbrother is also known as Lucy Marion.
The protesters scaled a 120ft (36.5m) lighting pole early in the morning and unfurled banners reading "One World One Dream Free Tibet" and "Tibet will be free".
The action was timed before the arrival of the Olympic torch in Tiananmen Square.
We have taken non-violent action at this critical time to draw the world's attention to the crisis gripping Tibet
Lhadon Tethong
Students for a Free Tibet
Clandestine Olympic protests
In London, fellow campaigners from the group also held a protest to coincide with the one in Beijing.
James Murray, 23, and Jenny Raynor, 26, climbed suspension cables to reach a height of 100ft (30m) above the River Thames and unfurled a banner saying: "Beijing 2008: Make Olympic History: Free Tibet."
In Beijing, Mr Thom spoke to the BBC by mobile phone while still suspended from the lighting pole.
He said: "I'm here today because I've been a long-term Tibet activist and I feel like now is a really critical time for Tibet.
"The Beijing Games have been used by the Chinese government as a propaganda tool to whitewash their human rights record in Tibet."
Consular access
The Olympics organising committee spokesman said the protest was "an illegal gathering".
He added: "We want to express our strong opposition to this. China has relevant laws regarding protests and gatherings. We truly hope that foreigners coming to visit China will respect the relevant laws of China."
The protest is under investigation, the British Embassy said.
"We are in touch with the Chinese authorities and are requesting immediate consular access should this information be correct," a spokesman added.
The Students for a Free Tibet group said further protests were likely during the games.
Dr Kerry Brown, an expert on Chinese issues with a London-based think-tank, Chatham House, said the Chinese authorities would be "very nervous, obviously, because of the opening ceremony tomorrow and they don't want to spoil that."
Activist explains the motive behind his protest
But Dr Brown added that if he was "brutally" honest, most Chinese were less concerned about the situation in Tibet than with their country's economy.
Friends of the Earth confirmed that Mr Thom worked for the organisation before leaving for Beijing. It called for his immediate release.
Mr Thom's father, Brian, told the BBC he was proud of what his son had done. He said his son had sent him a text message to say he was fine and being treated well.
Ms Fairbrother recently graduated from Bristol University and lives in London.
The Olympic torch has travelled 87,000 miles (140,000 km) through six continents since leaving Greece in March.
Its journey has been marked by protests about China's human rights record and its policies in Tibet.
During the month in which the torch began its progress, protests flared in Tibet against Chinese rule before snowballing into the worst unrest in Tibet for 20 years.
The Chinese Embassy could not be reached for comment.