From a packed Trafalgar Square, Cameron declared the £9.3 billion (US$15 billion) project a “great advertisement” for the country, before Jacques Rogge, the president of the International Olympic Committee, formally invited the world’s best athletes to compete in London next July.

“This has the makings of a great British success story,” Cameron said. “It’s on time and on budget.”

A day of celebration began in the Aquatics Centre and ended with the building hailed a “masterpiece” by Rogge and a “poem in concrete and steel” by Boris Johnson, the Mayor of London, who said that the water looked “good enough to drink — gin-clear.

Rogge, a Belgian surgeon not prone to hyperbole, said that he was “visually shocked” by a “fabulous” venue as he watched synchronized swimmers perform to a medley of Queen hits.

The series of events staged throughout the day — exactly 366 days before the opening ceremony (2012 is a leap year) — appeared to run smoothly as organizers shuttled between the Olympic Park and St. Pancras station, from where the Javelin train aims to transport 25,000 spectators an hour.

After greeting slightly bemused travelers from the Netherlands, France and Germany as they disembarked from the Eurostar, London 2012 chairman Sebastian Coe and Hugh Robertson, the Sports Minister, took off their shoes and socks to have their feet cast in clay. They then took the seven-minute journey to Stratford International on the Javelin train.