Jim Seida / NBC News

Metropolitan Police officers guard one of the entrances to London's Olympic Park on Monday. (Jim Seida / NBC News)

Updated at 9:09 a.m. ET: LONDON -- The biggest peacetime security operation in Britain’s history is under way – an $877-million civilian and military plan to protect athletes and visitors from threats ranging from suicide bombers to organized criminals. But it has also turned some London streets into military zones and Olympic venues into fortresses.

A simple glance at the main Olympic Park in East London confirms this will be the most security-conscious Games in history: More than 11 miles of razor-wire-topped electric fencing separates the site from its surroundings, every entrance is guarded by soldiers and the surrounding streets and shopping malls are patrolled by police carrying 9mm semi-automatic weapons – an unusual sight in Britain, where armed patrols are normally found only at airports.

On the busiest days, 12,500 police officers will be on duty while 12,200 soldiers will carry out the venue security searches assisted by at least 7,000 contracted civilian security workers. A further 5,500 troops will be involved in military operations outside the site.

“I think the British have prepared extremely well and in my judgment this is as secure an Olympics preparation as I have ever seen,” said NBC counter-terrorism expert Michael Leiter.

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Every vehicle entering the site is scanned and searched, inside and out, by military teams in ‘sterile’ zones away from key buildings. The maximum-security athletes’ village is ringed by even more metal fences. It’s enough to prompt some to compare the Olympic Park to a prison.

But it’s the less obvious measures that have brought the greatest controversy to the Games. At least 1,850 closed-circuit television (CCTV) cameras feed pictures back across London to the joint police and government control center (NOCC) at New Scotland Yard, the headquarters of the city’s Metropolitan Police, according to a data access request by civil liberties campaign group, Big Brother Watch. (Olympic organizers refused to say on Tuesday how many cameras are in use.)

The extent of the surveillance might surprise visitors from the United States, but is a common feature of life in Britain - the world’s biggest user of such technology with 4.2 million CCTV cameras in use by public agencies alone. 

As well as being fed through facial-recognition and license-place recognition software, images will be available to hundreds of CIA, FBI and TSA officials flying into Britain for the Games, as well as to officers from Interpol.

Jim Seida / NBC News

At least 1,850 security cameras keep watch on the Olympic Park.

Striking a balance between public protection and personal freedoms is increasingly difficult for authorities.

 “Of course the Olympics need to be secure but there is a danger of losing sight of all proportion,” Nick Pickles, director of Big Brother Watch, told NBCNews.com. "It would be a sad indictment of modern Britain if the lasting legacy of the Games is an unwarranted security and surveillance infrastructure.”

Slideshow: Olympic organizers keep a close eye on safety

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London puts in motion the largest peacetime security operation on British soil to ensure a seamless event.

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Drones
However, Chris Allison, assistant commissioner of the Metropolitan Police, on Tuesday insisted his force would be using “a light touch” in policing the Games – a promise borne out by armed officers posing for tourist pictures. (Officers have also been told not to run in response to emergency calls, to prevent panic among crowds.)

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The most contentious measure is the installation of six temporary high-velocity ground-to-air missile sites around East London, including two atop residential apartment blocks in Bow and Waltham Forest. Residents of the latter building lost a legal bid to have the weaponry moved.

Slideshow: Venues for 2012 London Olympic Games

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From Wimbledon to Wembley Stadium to The Dome, a look at the venues for the 2012 London Olympic Games.

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Unmanned drones – smaller, unarmed versions of those used by the U.S. to target Islamist militants in Pakistan and Afghanistan - will float above the venues, monitored by U.K. military commanders.

Helicopter-mounted cameras capable of identifying the color of a suspect's shoelaces on the ground from almost a mile away will also be utilized. The devices feature powerful zoom functions which can even allow airborne officers to see the color of a suspect's eyes on the ground.

For the first time since World War II, Britain’s Ministry of Defence has taken charge of London airspace, working alongside civilian air traffic controllers in Swanick, near Southampton, to ensure only aircraft with pre-approved flight plans are in the busy skies surrounding the capital’s key airports.

For the duration of the games, all airspace around the city is either restricted to pre-authorized private or commercial flight – or prohibited altogether.

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Four Royal Air Force Typhoon fighter jets on standby are prepared to intercept aircraft flouting the restrictions and use "lethal force" if necessary. Paul Haskins, general manager of London Terminal Control at air traffic control agency, NATS, told NBC News: “If an aircraft has not spoken to an air traffic controller for a long time and its coming a concern to ourselves and the military, various different methods will be used to communicate with that aircraft but if all those fail than an intercept will be provided by the military to ascertain exactly what is going on, on that flight.”

Britain's biggest warship, HMS Ocean, is also stationed on the River Thames, while Royal Fleet Auxiliary vessel Mounts Bay will be stationed near Weymouth, Dorset, where Olympic sailing events are taking place. Six helicopters - three Royal Navy Sea Kings and three RAF Pumas – complete the armory.

Despite the firepower, military officials want to downplay their presence. "We want the focus to be on [Jamaican sprinter] Usain Bolt this summer and not us," Air Vice-Marshal Stuart Atha told reporters in May.

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Security has been a fundamental issue for the London Games, literally from day one: the morning after the U.K. capital was named host city in 2005, a co-ordinated attack on buses and underground trains killed dozens in an atrocity referred to in Britain as 7/7.

Britain was America's closest ally in Afghanistan and Iraq, making it a prime target of Islamist terror groups. And dozens of recent terror plots, including the 2006 plot to blow up nearly a dozen trans-Atlantic airliners, have been hatched within Britain's sizeable Muslim population. 

'Tumultuous world'
Although other Olympics have taken place since 9/11 - Salt Lake City, Athens, Turin, Beijing and Vancouver - London offers a different breed of security challenge. 

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Many events are taking place at venues as far away as Scotland, creating a further security risk – that terrorists could avoid locked-down London and choose less high-profile targets instead.

"I'm confident that there is more than adequate security here for these games," Louis Susman, the U.S. ambassador to the U.K., told The Associated Press. "That said, we live in a tumultuous world, whether that be in New York or London." 

Britain’s terror level is currently labeled ‘Substantial’ - a notch below ‘Severe’, which has been the level for much of the past decade. A ‘Substantial’ threat level indicates an attack is a strong possibility. 

Despite the U.S.-U.K. collaboration, there will still be differences in how the London Olympics is policed. Most of the security personnel will be unarmed - a striking difference to operations in the United States. 

Adding to security issues, leaders from around the world will be in town. The American delegation will be led by first lady Michelle Obama while President Barack Obama focuses on his re-election campaign. 

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So far, the biggest wobble came earlier this month when private security contractor, G4S, admitted it would not be able to meet its target to supply the required number of civilian security workers – mostly because of the time taken to complete vetting checks of employment history and possible criminal backgrounds.

That story, first reported by NBC News’ Keir Simmons, prompted the government to summon 3,500 troops above the original 7,500 estimate. On Tuesday, the government announced a further 1,200 would be called in to guard against any possible security staff shortfall.  The extra troops, many of them called back from leave after serving in Afghanistan, are being housed in two temporary camps: One in a park near Hainault and another in Tobacco Dock, an empty commercial building in Wapping, near the Tower of London.

However, officials on both sides of the Atlantic remain confident. London's mayor, Boris Johnson, told Matt Lauer on TODAY on Wednesday: “The venues are as safe as we can make them. Politicians can never say the whole thing is 100 percent nailed down."

"The intelligence we’re getting is that the overall risk is being downgraded from severe to substantial, and the London Olympics will be as safe as any games has ever been,” he added.

"I've not heard any American who has said they were concerned about security here," said Susman, the ambassador. "London has made an effort to showcase London for the world and I think it's going to be terrific."

The Associated Press contributed to this report.

More world stories from NBC News:

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Slideshow: When the Olympics is your neighbor

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A diverse community in East London will welcome the world to Britain for the 2012 Olympic Games. Meet residents and hear how they feel about having a huge, world stage in their backyard.

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