Big Ben made sure the Olympic year was welcomed with a bang as hundreds of thousands of revellers were treated to a stunning display of fireworks launched from the tower at midnight.
In a first for the London's New Year celebrations, the pyrotechnics were fired from the landmark to coincide with each strike of the bell, marking the start of 2012.
There was a distinctly Olympian theme to the display on the River Thames with fireworks launched over the London Eye in the shape and colours of the Olympic rings. The accompanying soundtrack saw Chariots of Fire kick off a medley of London-themed songs.
Mayor of London Boris Johnson said: "Our New Year fireworks were a brilliant start to a spectacular year. This is just the beginning - as the eyes of the world turn to London for the Olympic and Paralympic Games, there will be amazing events across the capital up to, during and beyond a summer like no other."
About 250,000 people were estimated to be in the capital to watch the 11-minute and 15-second display, which saw 50,000 projectiles light up the capital's skies.
The Mayor of London's office said the display was the result of 12 months of planning. A crew of 306 has been working on the site since Boxing Day, with 1,803 staff - including stewards - on duty on the night itself. There were 30 tonnes of equipment on the three fireworks barges on the river ready for the display, which was triggered by GPS to the chimes of Big Ben.
Big crowds were also seen in other cities, including in Edinburgh for the Hogmanay street party attended by some 80,000 people. More than 20 acts were playing on seven stages ahead of the midnight fireworks display.
The start of the London fireworks display was accompanied by a recording of the moment the capital learned it would host next summer's Olympic and Paralympic Games. To coincide with the moment the city's name was read out, fireworks were launched around the London Eye.
Scotland Yard had 3,000 officers on duty both at street level and on podiums to give them a bird's-eye view of any troublemakers in the crowds. Scotland Yard later said officers patrolling the celebrations had made a total of 77 arrests by 4.30am. Chief Superintendent Julia Pendry said: "Crowds were good humoured and there were no major issues reported to police."
Meanwhile, The London Ambulance Service said it experienced a busy night, receiving calls peaking at 600 an hour - the average is usually 180 calls an hour on a normal night. By 3am paramedics had treated 274 patients and had taken 55 to hospital, the service said.