John Ray, who reports for ITV news, said he was pinned down by over-zealous authorities when a group of non-Chinese protestors unfurled a "Free Tibet" banner. He was then dragged along the ground and forced into a police van.
Ray said that the police also confiscated his equipment and accused him of attempting to display a protest flag.
The incident flies in the face of Chinese promises to allow international media to report freely during the games and is likey to embarrass the International Olympic Committee.
The incident occurred when several protestors gathered in the city's Ethnic Minorities Park near the main Bird's Nest stadium. When they started to unfurl a Tibetan flag, Ray and his crew attempted to film the group.
However, Chinese police pounced on the reporter, dragging him to a restaurant, where they sat on him. He was subsequently taken to a police van and was eventually released.
Ray's cameraman attempted to film Ray's assault, but was manhandled by police, who also used umbrellas to block his camera's view.
"I tried to explain to them that I was a British journalist but they would not even let me take out my identification documents," he told AFP. "They were very rough."