The Ministry of Defence says that similar missile defence systems have been deployed at all recent Olympic Games.
They will be in place by mid-July, along with Royal Navy helicopter carrier HMS Ocean (which will be moored in the River Thames), Royal Air Force Typhoon jets (which will be temporarily stationed at RAF Northolt), and Puma helicopters (at a Territorial Army centre in Ilford).
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A new pit filled with nothing but balls is helping visitors let off some steam.
"We do apologise", said Cote Brasserie.
Stomach-churning pictures released by Thames Water show a metal grill by silt and debris.