President Obama's security bubble

You can take the man out of the White House. But you can't take the White House away from the man.

And when US President Barack Obama arrives in London on Tuesday for the G20 summit, he will bring a large contingent of the White House staff with him.

Hundreds of security guards, doctors, chefs and others will accompany President Obama on his visit, and the entourage will include a number of presidential vehicles - including his new armour-plated limousine, The Beast, and aeroplane, Air Force One.

The 4,000 sq ft Boeing 747 is fully equipped for the president to work while he is in the air. The exercise-loving president will even be able to use the onboard gym to keep fit inflight.

The plane is fitted with some robust security equipment including shields to protect its instruments from an electromagnetic pulse. The communications equipment is even capable of withstanding radiation from a nuclear attack.

Blood supply

Once he lands at Stansted Airport in Essex, Mr Obama will be ferried into the heart of London on Marine One, his personal VH-3D helicopter.

Marine One is capable of firing flares to divert heat-seeking missiles - and always flies as part of a convoy of identical decoy aircraft. His helicopter peels away at the last minute only when the convoy has reached its destination.

On the ground, the president rides around in The Beast, a brand new presidential limo finished earlier this year at a cost of $300,000

It comes with a tear gas cannon, a night-vision camera and oxygen tanks. Its reinforced steel plating is said to be able to protect against bullets, chemical attack, and even a missile strike.

And it will not be hard to spot on the streets - it will be accompanied at all times by a motorcade consisting of dozens of support cars, police cars and emergency medical vehicles.

The president's White House medical unit - nurses, surgeons and other medical professionals - will be permanently on call in case Mr Obama is taken ill. A supply of AB-type blood (the president's blood type) will travel with him for emergency transfusions.

As well as medical personnel, Mr Obama's entourage will consist of over 200 security officials, dozens of political aides and a team of personal chefs.

Mr Obama will also be cooked for at 10 Downing Street by celebrity chef Jamie Oliver - although Mr Oliver has been told that he will not be allowed to bring his mobile phone, even though his wife is due to give birth on the day after the event.

For security reasons, no mobile devices will be allowed at the dinner.

World leaders

During his visit, Mr Obama will spend three hours in talks with the British Prime Minister, Gordon Brown.

And - as is customary on presidential visits to the capital - Mr Obama will also meet the opposition leader, David Cameron, and will hold a private meeting with the Queen.

As well as the main G20 summit, the president will fit in bilateral meetings with a number of world leaders - including Russian President Dmitry Medvedev, Chinese President Hu Jintao, Indian Prime Minister Manmohan Singh, South Korean President Lee Myung-bak and King Abdullah of Saudi Arabia.

With the world economy in turmoil, and the US fighting wars on several fronts, these meetings will be crucial.

So it is easy to see why Mr Obama needs such a large back-up team to keep his presidential bubble inflated while he focuses on doing his job.