A massive police and military operation is on standby just three weeks before the London Olympics with fighter jets, combat helicopters, thousands of police and the Royal Navy's largest warship stationed on the Thames in the capital during the games.
That heightened security – and nervousness around a high-profile attack in Britain – has resulted in three separate security incidents in the span of 24 hours as authorities leave nothing to chance.
On Friday, police announced the arrests of seven men on suspicion of terrorism offences after weapons were found in their vehicle when it was pulled over in a routine stop in northern England.
In early morning raids on residences in London on Thursday, anti-terrorism police arrested six people suspected of being involved in a plot against British targets. Security officials said the plot was not linked to the Olympics.
In the second incident, which proved to be a false alarm, dramatic TV scenes showed armed police investigating bus passengers one-by-one in an early morning incident that blocked traffic in both directions on a major British highway 187 kilometres north of London. British ministry of defence personnel provided police support. The incident was later described as not being terror-related.
The current security budget estimate of $870-million has already been doubled and is expected to climb significantly by the time the Olympics and Paralympics are finished. The 2010 Vancouver Olympics security ballooned to $900-million.
The total Olympics budget is set at $14.7-billion – nearly four times the 2005 estimate given by organizers when London won the 2012 bid.
Concern over a terror attack tops the list of threats, but authorities are also concerned about organized crime and protests similar to those that took place over three days last August in London and other major cities.
To stop a terror attack, a significant military operation is in place.
Fighter jets and helicopters will protect the airspace over the London Olympics, surface-to-air-missiles will be stationed on top of residential buildings, and 12,500 police will be on the ground during the games with 23,000 part-time security guards at sporting venues.
A security exercise in May saw the Royal Navy's largest warship HMS Ocean, which is a landing platform for six helicopters, moored on the Thames River at Greenwich. It will be overseeing marine security during the games.
This video filmed in May shows the warship, which resembles an aircraft carrier, squeezing through the central gate of the Thames Barrier, a flood barrier meant to protect London from flooding, on its way to take part in security preparations.
Thirty-two kilometres west of the Olympic Stadium in east London, Royal Air Force Typhoon jets will be on stand by at RAF Northolt in the event of a 9/11-type air threat to London.
Puma combat helicopters will be stationed at an army facility six kilometers to the east of stadium and other Olympics venues.
Most controversially, a decision to station surface-to-air-missile batteries on the rooftops of apartment blocks in east London will go ahead. Residents have criticized the decision over a lack of consultation and anxiety over the prospect of missiles being placed on 'top of their heads.' A high court challenge by residents may yet quash the missile plan.
Missiles would be used if an air threat was not intercepted by one of the fighter jets patrolling the skies.
In May, a British tabloid reported that it had smuggled a fake bomb past security checkpoints in to an area where the key sporting facilities have been built. The driver of a mechanical digger carried the harmless device in to main Olympics area.
"If I had terrorist connections I could be bringing in explosives, chemicals – anything at all," he told the British tabloid.
Olympics organizers explained that the main area and the athletes village would be "searched and sealed" before being locked down ahead of the July 27 opening ceremony. Most police will not be armed and street-level security will be police-led, with armed police or soldiers only being deployed in the event of an incident.