A series of airspace restrictions around London and south-east England are set to be enforced as part of security for the 2012 Olympic Games.
The Ministry of Defence said equipment and personnel from the Royal Navy, Army and Royal Air Force will be in place from tomorrow to secure the area.
It comes as it emerged that 3,500 extra service personnel would be needed to bolster security at the Olympics.
Defence Secretary Philip Hammond said the Games will be "safe and secure".
The prohibited zone will be about 30 miles wide and does not affect commercial aircraft, which fly in established air traffic corridors.