The biggest protests since the flame was lit two weeks ago in Greece underscored human rights concerns and tarnished the Asian powerhouse's plans for a harmonious display of pomp and sport ahead of the summer games in Beijing.
Frantic organizers shuffled the relay's participants and made on-the-spot changes on the course to avoid confrontations with demonstrators, who waved Tibetan flags, clashed with police and grew bolder as the event progressed. Roughly 2,000 police officers kept the flame moving in face of repeated onslaughts.
Police say 37 people have been arrested for a range of public order offenses.
Along the route, hundreds of protesters jeered the hand-offs and chanted "Free Tibet!" "Stop killing in Tibet!" "China, talk to Dalai Lama!"' and waved placards condemning the country's role in Darfur.
"They've called the torch relay a journey of harmony, but on the ground in Tibet they are shooting and killing peaceful Tibetan protesters," said Matt Whitticase, a spokesman for the London-based Free Tibet Campaign. "We want to use the momentum gathered over this weekend to really press our case that the torch should not be allowed to be paraded triumphantly by China."
Activists demonstrating against China's human rights record and a recent crackdown in Tibet have been protesting along the torch route since the start of the flame's 85,000-mile odyssey from Ancient Olympia in Greece to Beijing, the host of the 2008 Summer Olympics.
The torch's global tour - the longest in Olympic history - is part of China's drive to highlight its growing economic and political power through the Olympics. But it also has offered protest groups abundant opportunity to draw attention to their concerns.
"There was definitely a bit of an edge," British tennis player Tim Henman, one of the torchbearers, told The Associated Press.
The trouble began early in the day as a spring snowfall uncharacteristically blanketed the capital. Demonstrators attempted to board a relay bus shortly after five-time Olympic gold medalist Steve Redgrave started the procession at Wembley Stadium.
In west London, a protester tried to grab the torch out of the hands of a diminutive children's television host, forcing police to briefly stop the procession. Another demonstrator tried to snuff out the flame with what appeared to be a fire extinguisher. Others simply threw themselves out of the crowd and into the flame's path.
British Prime Minister Gordon Brown briefly greeted the torch when it arrived outside his Downing Street residence as pro-Tibet demonstrators and police clashed yards away near Britain's Parliament buildings. Brown never handled the torch, but watched as Olympic gold medalist Denise Lewis handed it to Paralympic hopeful Ali Jawad.
Demonstrators swelled in number near the spot where Chinese Ambassador Fu Ying had been expected to carry the Olympic torch. Instead, Fu emerged with the torch in the heart of London's Chinatown, managing to jog unhindered before handing it over to the next participant.
The ugliest scenes occurred between Trafalgar Square and the iconic Big Ben clock tower. A dozen protesters charged the torch and police reacted with force, shoving aside anyone who appeared to threaten the torch's path.
"Everyone was running at (me). It was a bit weird," said Scott Earley Jr., 17, the torchbearer at the time. "The police had it covered. They told me when to go and what to do."
About 100 demonstrators managed to briefly impede the flame's progress by surrounding it near St. Paul's Cathedral, forcing police to put the flame-bearer on a bus before continuing.
Some protesters complained about police tactics. Authorities corralled Tibetan protesters in metal barricades across from Bloomsbury Square, not far from the British Museum, forcing anyone with Tibetan paraphernalia into the area.
"It really hurts," said Passang Dolne, 27, a Tibetan national who works as a nurse in London. "It feels like we are restrained like a sheep in a barn. We are not allowed to get out."
Meanwhile, Chinese nationals who gathered roughly 100 yards away were allowed freedom of movement as they waved Chinese flags distributed by the Chinese Embassy and the Bank of China.
"We don't like the Tibet people who use this time against the Chinese. It's not a proper venue," said Ting Yan, 27, who is originally from southwest China but is in London working for a telecommunications firm.
But some, like Chinese student Yanning Yang, who traveled from outside the capital to support the torch relay, said protest was inevitable.
"Whatever the protests is, you can't be undermined in violence," she said. "We accept criticism and there is a lot we need to improve."
Lianna Hulbert, 23, of London, who carried a placard denouncing China's support for the Sudanese regime, said the demonstrators were doing what others cannot elsewhere.
"This is a place where people can be the voice of the voiceless," she said.