Court number one at the Old Bailey and Central London is the most famous courtroom in the world.

The venue for many of the most sensational criminal trials in history.

On top of the domed building, a bronze statue of Lady Justice holds a sword in her right hand

and the scales of justice in her left.

From the cells and the bowels of the building, a wiry man in an oversized grey suit

is led by a pluse man up a narrow dark staircase.

Pins are neatly lined in his breast pocket.

The defendant emerges into the bright white light of the courtroom

and is greeted by a row of somber faces.

The charges are so sensitive there's no jewellery.

On the bench sits Judge Lord Rainer Goddard, a man with a fearsome reputation

and a firm advocate of capital punishment.

He describes himself as an avenging enemy of criminals and a vigilant Lord protector of society.

As the defendant takes this all in, he briefly touches his breast pocket

to fill the neat line of pen stored there.

But as Klaus Fuchs looks around the court, he's not the only man with shredded nerves.

Unbeknown to him, the prosecution's case against him is precarious.

For eight years he was spying for the Soviet Union, handing them all the secrets he could

as an atomic physicist inside the British and American nuclear bomb programs.

The main indisputable evidence against Fuchs is too secret to be revealed.

He may have confessed, but even that is not water time.

If he now pleads not guilty, he will almost certainly walk free.

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