Thirty-seven arrests have been made after clashes between pro-Tibet protesters and police as the Olympic torch made its way through London.
Protests over China's human rights record began soon after the relay began at Wembley, and prompted an increasing police presence through the city.
One protester tried to snatch the torch from former Blue Peter host Konnie Huq.
After an unpublicised change to the route, the Chinese ambassador carried the torch through Chinatown.
It later made an unscheduled move onto a bus.
A protective ring of 10 Chinese flame attendants and fluorescent-jacketed police officers surrounded the torchbearers at all times, with additional uniformed officers joining at potential flashpoints along the route.
Police decided the torch should travel along Fleet Street to St Paul's Cathedral by bus, rather than held by a runner, after it was surrounded by a large group of protesters.
A contingent of pro-China supporters also tried to make their voices heard along the route, waving Chinese and Olympic flags and calling for "one China".
Outside Downing Street there were chaotic scenes as former Olympic heptathlon gold medallist Denise Lewis took the flame to No 10.
Gordon Brown greeted the torch outside Number 10 despite coming under pressure to boycott the parade and the Beijing Olympics opening ceremony. However he did not hold it.
Liberal Democrat leader Nick Clegg said the prime minister's involvement was "wholly inappropriate" until China opened talks with the Dalai Lama.
Police said there were about 500 people in Whitehall and about 2,000 gathered near the British Museum.
Several small scuffles broke out as police tackled some of the protesters.
Beijing Olympic torch relay spokesman Qu Yingpu told the BBC: "This is not the right time, the right platform, for any people to voice their political views.
"So we are very grateful and very thankful to the people in London, the police and the organisers, for their efforts trying to keep order."
Pictures of the London relay were broadcast on China's state-controlled TV, but not of the protests and disruption.
Metropolitan Police Commander Jo Kaye denied officers had been heavy-handed with some protesters.
"Our duty is to see that that torch is taken safely and securely to the end of its route. We're doing that. We're on schedule. The convoy has kept going according to schedule all the way," he said.
"People cannot just come in and cause havoc with what's being done there and the officers have stopped them. They know quite well that they shouldn't be trying to get in at the torch and they've been stopped."
At the start of the relay, three protesters were taken away by police after trying to board the open-top bus taking the torch from Wembley.
Police also stepped in when a protester later tried to snatch the torch from Ms Huq.
She told BBC News 24 she was "a bit bashed about" but not seriously hurt.
"I always said my taking part in the procession doesn't mean I condone China in any way," she added.
"I believe in the Olympic values, the Olympic ideals... it's just unfortunate that China has such a terrible track record when it comes to human rights and they are the host nation."
Those taking part in the relay include 10 Olympic champions, 18 schoolchildren and public figures such as news reader Sir Trevor McDonald and musician Vanessa Mae.
Double Olympic champion Dame Kelly Holmes ran the last stage of the route to complete the relay and lit the Olympic cauldron in front of 5,000 spectators.
The flame will complete the London leg of its journey with a finale event at the O2 Arena. It will then leave for Paris.
Girl band The Sugababes withdrew from the finale at the last minute, saying singer Amelle Berrabah had been diagnosed with laryngitis. They had earlier carried the torch on an open top bus down Oxford Street.
The torch was lit in Olympia, Greece, last week and will go through 20 countries before being carried into the Beijing Games opening ceremony on 8 August.
LONDON TORCH RELAY 6 APRIL
1: Wembley 1030BST
2: Ladbroke Grove 1100
3: British Museum 1220
4: China Town 1230
5: Trafalgar Square 1250
6: Southbank Centre 1330
7: Somerset House 1415
8: St Paul's Cathedral 1430
9: Potter's Fields 1500
10: Whitechapel Road 1530
11: Stratford 1600
12: Canary Wharf 1700
13: North Greenwich 1800
Source: Mayor of London