The London Olympics will have the toughest anti-doping program in history, 2012 chief Sebastian Coe said on Tuesday as officials prepared for the one-year countdown to the sporting showpiece.

Speaking in a conference call with journalists on the eve of Wednesday's one year-to-go milestone, Coe said drug testers at London 2012 would be equipped with the most sophisticated anti-doping technology of any Olympics in history.

"What I can say to athletes coming to London is that we will have the technology in place that is in excess of any technology that you have ever encountered anywhere in the world," London 2012 chairman Coe said.

"You come to London and you try that, we will get you," Coe warned, citing the triple-pronged enforcement strategy of the International Olympic Committee (IOC), London 2012 organizers and the British police.

"It's the number of tests, it's the vigilance, it's the technology," Coe said, while acknowledging no Olympics was likely to be drug-free.

"I am absolutely realistic that there will always be people in sport that will want to step beyond the boundaries, legal and moral that we set ourselves, and it is for us to be eternally vigilant.

"Can I guarantee an entirely clean Games? The answer is no, but we will do everything in our power to make that happen."

Olympic officials have already indicated their determination to crack down on the use of syringes outside medical areas while IOC chief Jacques Rogge has said the fight against doping remains the organization's top priority.

Rogge was among the dignitaries in London on Wednesday as the city formally began the one-year countdown to the 2012 Games, which get under way on July 27 next year.

Rogge issued an invitation to athletes to compete in London at an evening ceremony in Trafalgar Square while British diver Tom Daley performed the first dive at the Olympic Park's Aquatics Centre.

Wednesday's events also provided the first glimpse of how London will look when key buildings and parts of the city are "dressed" for the Games.

"It is a big day for us," Coe said. "One year to go is a defining moment in the history of an Olympic Games.

"Jacques Rogge will in essence be formally inviting the world to the Games, and we want to be able to show the world that we're getting ready to host them."

"We are fully on track, we are on schedule, and we are within budget with one year to go and I take particular pride in that," Coe said.

"It's a project of infinite complexity and I'm happy to report we're in good shape."

Coe, meanwhile, said he wanted the London Games to be a fusion of some of the most successful recent Olympics.

"I want the party atmosphere of Sydney (2000), the spirit of humanity of Barcelona (1992) and the forensic eye for detail we saw in Beijing (2008)," he said.