Armed British police stand guard at Terminal 1 at Heathrow Airport on July 17th 2012, as athletes and officials arrive for the London 2012 Olympic Games. The Games will begin officially on July 27. AFP PHOTO / WILL OLIVER

British military personnel walk past the Olympic Stadium ahead of the London 2012 Olympic Games in the Olympic Park in east London on July 17, 2012. Britain's military is to provide up to 3,500 extra troops for security duty at the Olympic Games, after the private security firm G4S admitted that it would not be able to supply enough personnel. The overall 23,700-strong security force will include a mix of military, private security guards and at least 3,000 unpaid volunteers. AFP PHOTO / MIGUEL MEDINA

British police dog handlers patrol with their sniffer dogs Heathrow airport terminal 4 in west London on July 16, 2012 as officials and athletes arrive in the capital for the London 2012 Olympic Games. AFP PHOTO / ANDREW COWIE

A London 2012 games maker stands ready at Heathrow airport terminal 4 in west London on July 16, 2012 as officials and athletes arrive in the capital for the London 2012 Olympic Games. AFP PHOTO / ANDREW COWIE

Armed police patrol around the athletes village at the Olympic Park site in Stratford, east London, on July 16, 2012. AFP PHOTO / POOL / John Stillwell

Members of the Armed Forces are shown around the site of the London 2012 Olympics in east London on July 15, 2012. Following the failure of contracted security firm G4S to provide the 10,000 trained security for the events, the Armed Forces have been drafted in to assist with security operations. The G4S group yesterday admitted that they will be funding the cost of this coverage and are set to make a loss of up to L50million on the contract. AFP PHOTO / LEON NEAL

Members of the Armed Forces are shown around the site of the London 2012 Olympics in east London on July 15, 2012. Following the failure of contracted security firm G4S to provide the 10,000 trained security for the events, the Armed Forces have been drafted in to assist with security operations. The G4S group yesterday admitted that they will be funding the cost of this coverage and are set to make a loss of up to L50million on the contract. AFP PHOTO / LEON NEAL

Britain's helicopter carrier HMS Ocean, the Royal Navy's largest ship, is pictured on July 14, 2012 in Greenwich, southeast London, where it will be used during the Olympic Games as a base for helicopters and military personnel. The London 2012 Olympic Games will begin on July 27, 2012. AFP PHOTO / CARL COURT

TOPSHOTS Lance Corporal Alex Walton (L) and Corporal Dan Best of the RAF Regiment take part in a media facility at RAF Northolt in west London on July 13, 2012 to show off some of the aircraft and equipment that will be used to protect the London during the upcoming Olympic Games. A series of airspace restrictions around London and south-east England are set to be enforced from midnight. AFP PHOTO / LEON NEAL

Lance Corporal Alex Walton (L) and Corporal Dan Best of the RAF Regiment take part in a media facility at RAF Northolt in west London on July 13, 2012 to show off some of the aircraft and equipment that will be used to protect the London during the upcoming Olympic Games. A series of airspace restrictions around London and south-east England are set to be enforced from midnight. AFP PHOTO / LEON NEAL

Corporal Dan Best of the RAF Regiment takes part in a media facility at RAF Northolt in west London on July 13, 2012 to show off some of the aircraft and equipment that will be used to protect the London during the upcoming Olympic Games. A series of airspace restrictions around London and south-east England are set to be enforced from midnight. AFP PHOTO / LEON NEAL

Britain's helicopter carrier HMS Ocean, the Royal Navy's largest ship, sails into Greenwich in London, on July 13, 2012, as it prepares to anchor on the River Thames, in southeast London. It will be used during the Olympic Games as a base for helicopters and military personnel. The London 2012 Olympic Games will begin on July 27, 2012. AFP PHOTO/WILL OLIVER

Specialist police dog 'Chester' searches Victoria Coach Station in central London, on July 12, 2012, in the run up to 2012 London Olympic Games which starts on July 27, 2012. AFP PHOTO / SANG TAN/POOL

The British Royal Navy Helicopter Carrier HMS Ocean is towed through the Thames Barrier in east London as it heads towards Greenwich on May 4, 2012 to take part in the major military and civilian security exercise "Olympic Guardian" ahead of the Olympic Games. HMS Ocean, Britain's largest ship, will be stationed at Greenwich in east London for the duration of the Games as a maritime logistics hub and helicopter launch pad supporting a massive operation aimed at securing London 2012. AFP PHOTO / LEON NEAL

Two girls watch the British Royal Navy Helicopter Carrier HMS Ocean as it is towed through the Thames Barrier in east London heading towards Greenwich on May 4, 2012 to take part in the major military and civilian security exercise "Olympic Guardian" ahead of the Olympic Games. HMS Ocean, Britain's largest ship, will be stationed at Greenwich in east London for the duration of the Games as a maritime logistics hub and helicopter launch pad supporting a massive operation aimed at securing London 2012. AFP PHOTO / LEON NEAL

A British Royal Navy Lynx helicopter pilot talks to a crew member after landing on helicopter carrier HMS Ocean during security rehearsals, "Exercise Olympic Guardian", ahead of the London 2012 Olympic Games in the Thames estuary, east of London, on May 4, 2012. HMS Ocean, Britain's largest ship, will be stationed at Greenwich in east London for the duration of the Games as a maritime logistics hub and helicopter launch pad supporting a massive operation aimed at securing London 2012. AFP PHOTO/ BEN STANSALL

British Royal Navy Lynx helicopter sits on the deck of helicopter carrier HMS Ocean during security rehearsals, "Exercise Olympic Guardian", ahead of the London 2012 Olympic Games in the Thames estuary, east of London, on May 4, 2012. HMS Ocean, Britain's largest ship, will be stationed at Greenwich in east London for the duration of the Games as a maritime logistics hub and helicopter launch pad supporting a massive operation aimed at securing London 2012. AFP PHOTO/ BEN STANSALL

A soldier from the Royal Artillery looks on as a Rapier missile defence system, which could play a role in providing air security during the Olympics, is shown to members of the media at Blackheath in southeast London on May 3, 2012. Britain is to rehearse its security measures for the Olympic Games this week in a military exercise involving warships, fast jets, helicopters and dummy missiles, the Ministry of Defence said. Exercise Olympic Guardian, a land, sea and air drill, will take place in three phases from May 2-10 -- the first on the south coast, the second in London's airspace and the final phase on the River Thames. AFP PHOTO/CARL COURT

A Rapier missile defence system, which could play a role in providing air security during the Olympics, is shown to members of the media at Blackheath in southeast London on May 3, 2012. Britain is to rehearse its security measures for the Olympic Games this week in a military exercise involving warships, fast jets, helicopters and dummy missiles, the Ministry of Defence said. Exercise Olympic Guardian, a land, sea and air drill, will take place in three phases from May 2-10 -- the first on the south coast, the second in London's airspace and the final phase on the River Thames. AFP PHOTO/CARL COURT

A Starstreak high velocity missile (HVM) system, which could play a role in providing air security during the Olympics, is manned by members of the British Royal Artillery during a media demonstration at Blackheath in southeast London on May 3, 2012. Britain is to rehearse its security measures for the Olympic Games this week in a military exercise involving warships, fast jets, helicopters and dummy missiles, the Ministry of Defence said. Exercise Olympic Guardian, a land, sea and air drill, will take place in three phases from May 2-10 -- the first on the south coast, the second in London's airspace and the final phase on the River Thames. AFP PHOTO/CARL COURT

A Starstreak high velocity missile (HVM) system, which could play a role in providing air security during the Olympics, is manned by members of the British Royal Artillery as a Rapier ground-based air defence (GBAD) system stands in the backround (R) during a media demonstration at Blackheath in southeast London on May 3, 2012. Britain is to rehearse its security measures for the Olympic Games this week in a military exercise involving warships, fast jets, helicopters and dummy missiles, the Ministry of Defence said. Exercise Olympic Guardian, a land, sea and air drill, will take place in three phases from May 2-10 -- the first on the south coast, the second in London's airspace and the final phase on the River Thames. AFP PHOTO/CARL COURT

A general view shows the Lexington Building in east London on May 2, 2012, one of the proposed sites for the deployment of Ground Based Air Defence (GBAD) systems as part of the security provisions for the London 2012 Olympic Games. The Ministry of Defence announced on April 30 that six sites in London were being considered for the siting of missile systems during the Games. According to the MOD the converted water tower at the Lexington Building had been identified as a potentional location for the deployment of High Velocity Missile (HVM) systems to compliment the ground based Rapier units that might be deployed elsewhere. AFP PHOTO / MIGUEL MEDINA

Chinook Helicopters fly over the Olympic Stadium in London on May 2, 2012. London launched a major military exercise Wednesday to check security responses for the 2012 Olympics, as the final wave of test sports events got under way. AFP PHOTO / GLYN KIRK

Metropolitan police officers look toward the Olympic Stadium from the entrance to the swimming venue ahead of the FINA Olympic Games Synchronised Swimming Qualification competition, a part of the London Prepares series of test events, at the Aquatics Centre in the Olympic Park in London on April 20, 2012. AFP PHOTO / ADRIAN DENNIS

A British Royal Air Force E-3D Sentry AEW aircraft carrying Defence Secretary Philip Hammond lands at RAF Waddington near Lincoln, England on February 29, 2012, as he arrives to observe a London 2012 Olympic Games air security training exercise, codenamed Exercise Taurus Mountain 2. Aircraft including RAF Typhoon interceptors, RAF E-3D Sentry and RN Sea King surveillance aircraft, sniper-carrying RAF Puma and RN Lynx helicopters took part in the exercise. AFP PHOTO / ANDREW YATES

British Defence Secretary Philip Hammond (L) talks with a crewman as he observes an Olympic training exercise codenamed Exercise Taurus Mountain 2 during a flight in a E-3D Sentry aircraft at RAF Waddington, near Lincoln, England on February 29, 2012. AFP PHOTO / POOL / RUI VIEIRA

A simulated casualty is evacuated during an emergency services drill in preparation for the London Olympics entitled Exercise Forward Defensive at the disused Aldwych underground station in London on February 22, 2012. The drill was a major exercise to test the emergency service and Government response to a terrorist incident during the Olympic and Paralympics Games. AFP PHOTO / BEN STANSALL

A simulated casualty is evacuated during an emergency services drill in preparation for the London Olympics entitled Exercise Forward Defensive at the disused Aldwych underground station in London on February 22, 2012. The drill was a major exercise to test the emergency service and Government response to a terrorist incident during the Olympic and Paralympics Games. AFP PHOTO / BEN STANSALL

A simulated casualty is evacuated during an emergency services drill in preparation for the London Olympics entitled Exercise Forward Defensive at the disused Aldwych underground station in London on February 22, 2012. The drill was a major exercise to test the emergency service and Government response to a terrorist incident during the Olympic and Paralympics Games. AFP PHOTO / POOL / STEFAN ROUSSEAU

Members of the emergency services evacuate a mock casualty during a security drill in preparation for the London Olympics entitled Exercise Forward Defensive at the disused Aldwych underground station in London on February 22, 2012. The drill was a major exercise to test the emergency service and Government response to a terrorist incident during the Olympic and Paralympics Games. AFP PHOTO / BEN STANSALL

The Metropolitan Police and Royal Marines in offshore landing craft, rigid inflatable boats (RIBs), a Lynx helicopter and other craft speed along the river Thames near Woolwich during a safety and security planning exercise for the London 2012 Olympic Games in London on January 19, 2012. The Royal Marines joined 44 police officers in a police-led safety and security exercise in preparation for the Games in London. AFP PHOTO / ADRIAN DENNIS

British security personnel speed along the river Thames near Woolwich during a safety and security planning exercise for the London 2012 Olympic Games in London on January 19, 2012. The Royal Marines joined 44 police officers in a police-led safety and security exercise in preparation for the Games in London. AFP PHOTO / BEN STANSALL

A Royal Navy Lynx helicopter hovers of a passenger ferry on the Thames near Woolwich during a safety and security planning exercise for the London 2012 Olympic Games in London on January 19, 2012. The Royal Marines joined 44 police officers in a police-led safety and security exercise in preparation for the Games in London. AFP PHOTO / BEN STANSALL