Just a day earlier, the city exulted in the triumph of winning the 2012 Olympic games. But jubilation turned to shock and revulsion Thursday, when a volley of bomb blasts wrought havoc in rush-hour London, killing at least 33 people, wounding 350 more, and bringing home forcefully that the British capital is a frontline in the war on terror.
Even as the country reeled from its worst-ever terrorist attack, comforting qualities of calm, bravery, determination, and solidarity shone through the hazy dismay.
London may be no stranger to terrorism following its long history of attacks from the Irish Republican Army, but it has never witnessed such a coordinated wave of violence in peacetime. Comparisons were quickly drawn with the attacks on Madrid trains last year that killed 191, and authorities could not rule out an escalating death count, particularly as the bus toll had not been assessed.
A little-known group apparently affiliated with al Qaeda claimed responsibility. Police said it was unclear whether suicide bombers were involved. Experts said the lack of warning, the coincidence with the G-8 summit, and the nature of the attacks resembled previous attacks by radicals professing to act in the name of Islam.
Londoners have long been bracing for such scenes. Police say they have already foiled several attacks, and have warned that terrorists would probably get through sooner or later. Attacks in November 2003 on British interests in Istanbul were taken as a warning sign.
Police and emergency services have stepped up training to deal with precisely this sort of scenario. "Ever since 9/11 we had a review of our plans, and have worked on various scenarios like this," says David Henson, a police spokesman.
Despite such preparations, Thursday's attacks exposed the acute difficulties authorities face in combating terrorism in one of Europe's best-prepared cities.
"Both the method of attack and the timing of this incident were completely predictable," says Charles Shoebridge, a former counterterrorism intelligence officer. "This incident shows that irrespective of previous successes in thwarting attacks, there was a major failure to predict and prevent the attack.
"If you do not have intelligence beforehand of an attack, this kind of incident is difficult to prevent - in mass transportation systems it is impractical to have searches and screening," he adds.
Yet few people were expecting a backlash against the authorities. Anger against the Iraq war bubbles below the surface here, and a certain frustration has emerged in protests at the G-8 in Scotland.
But Sam Hardy, an analyst at Royal Institute of International Affairs, says: "The British people won't lay any blame at the door of Tony Blair."
"There will be some who link this to the war in Iraq, but the initial response will be more in terms of solidarity - with the government and with your neighbor - rather than laying blame," Mr. Hardy adds.
London is home to large Islamic communities. Some British Islamic groups condemned the attacks. Sir Iqbal Sacranie of the Muslim Council of Britain said: "These terrorists, these evil people want to demoralize us as a nation and divide us. All of us must unite in helping the police to hunt these murderers down."
But other Muslims here took a hard line on the attack. "Muslims around the world are being oppressed by the West. Do you expect Muslims just to lie down and die or do you expect them to fight?" says one watchmaker. "I do not think that this will help the Muslims in Britain - it will only make things difficult. After 9/11 and the bombings in Madrid, life became more difficult for us," he says.
Though the city was shocked, many people were not surprised. Londoners know they are a terrorist target, principally because of Britain's support for the Iraq war. Police have even said a terror strike was not a question of "if" but "when."
"When" turned out to be at 8:51 a.m. near the busy Liverpool Street Tube (subway) and rail hub in the financial district. Two further explosions detonated in the Tube, trapping many hundreds of commuters underground for up to half an hour in acrid smoke and semi-darkness. A fourth ripped open a bus like a sardine tin.
"There were people walking everywhere, home, to work, or to find buses," said one witness caught up in the mayhem that followed the attacks. "Everyone was so matey. There was a mile-long queue for taxis, but people were just calmly standing there, helping each other."
London's police chief, Sir Ian Blair, said it was certainly a coordinated strike and told people to stay put. A grim Tony Blair said the assault had been planned to coincide with the critical G-8 summit he is hosting in Scotland.
"Here at this summit, the world's leaders are striving to combat world poverty and save and improve human life," he said. "The perpetrators of today's attacks are intent on destroying human life. The terrorists will not succeed."
The city was rapidly shut down. Usually busy streets took on an unfamiliar aura, peopled by bewildered survivors, stray commuters, and concerned onlookers. Buses and trains stopped. Traffic disappeared altogether from some districts. A fine drizzle settled over the mayhem. Telephone networks became fitful. Financial markets tanked. The queen said she was "deeply shocked."
Victims spoke of being caught amid scenes usually only witnessed on their television screens.
• Don Kirk and James Brandon in London contributed to this report.