President Bush's every movement is being monitored from a high-tech command centre in Scotland Yard, headquarters of London's Metropolitan Police.
Up to 100 officers at a time occupy the windowless control room in the bowels of the office block halfway between Victoria railway station and the Houses of Parliament. They have access to live feeds from more than 600 cameras around the capital which appear on a bank of 20 monitors along one wall.
Commander Mike Messinger - designated the chief or "gold" officer for the operation - sits in front of the screens surrounded by a team of tactical advisers. He is in constant radio communication with senior officers on the ground.
Areas where Mr Bush is staying or travelling through have been divided up into more than half-a-dozen sectors. A special team sitting at semi-circular metallic computer stations has been assigned to co-ordinate the security operation in each sector.
Each team has its own separate radio frequency for communicating with officers on the street in its sector. The frequencies are separated to avoid confusion on the ground or overload on radio systems.
At another desk, officers from the special security group, army liaison, air support units, the diplomatic protection group and Special Branch follow the president's movements on two wide screen televisions and a projection screen. Another desk is home to the "info cell" which co-ordinates undercover officers on the ground, who also have their own radio frequency.
A small number of officers from British Transport Police and City of London Police are also stationed in the nerve centre with London Ambulance and Fire Brigade in a room next door.
A half-dozen strong team of dedicated traffic officers monitors flow on the roads using digital maps and cameras.
Officers in the special operations room - veterans of other large-scale policing events, such as May Day, the Notting Hill carnival and anti-war protests - say Mr Bush's visit is their biggest challenge so far.
More than two months of planning have gone into staffing arrangements in a bid to ensure no one works more than a 12-hour stretch, which could lead to officers not being as alert as they should be.
Over a 24-hour period, up to 200 people are involved in running the room at the heart of the security operation. Senior officers are in constant 24-hour contact with the huge team of Secret Service agents brought to Britain by Mr Bush.
In an adjacent room calls from the public about the effects of the visit are fielded. Since Monday, more than 1,000 phone calls and 1,500 e-mails have been handled from people inquiring about road closures and other aspects of the state visit.