A British high court judge from the Thirties named John Sankey once described the presumption of innocence as "the golden thread" that runs throughout any criminal justice system.

What it means is simple. Anyone accused of any kind of crime is judged to be innocent until proved guilty. And the onus is on the accuser, society, not the accused, to prove the case.

It has been part of human law almost from the beginning of courts.

The Prophet Mohammed preached the presumption of innocence as set down in the Koran and Sharia law. Roman law did the same. It said: "Proof lies on him who asserts, not on him who denies."

But it's a fragile concept, this golden thread. It can be easily broken. Accused persons can be tried and found guilty in the media, for example, before ever setting foot in a courtroom.

But what about in the courtroom itself?

If you've ever been in a Canadian court, you will know that the accused sits in a box called the prisoner's dock. He or she is separated from defense counsel and often there are constables on either side.

In the U.S., it is entirely different. The accused sits at a table beside the defense lawyer.

And in the U.S., the accused are normally dressed in street attire, not prison garb. In Canada, the accused are often dressed in jailhouse orange jumpsuits.

Does the sight of a prisoner in the dock, dressed in prison garb, prejudice a jury and the whole idea of presumption of innocence?

I think it does. I think the sight of a prisoner in the dock, perhaps in jailhouse orange, immediately suggests to a juror that the accused is guilty.

William Trudell is an eminent defense lawyer who for 40 years has acted for people accused of a crime. He is also chair of the Canadian Council of Criminal Defence Lawyers. This week I put these questions to him.

On the question of the prisoner sitting in a dock, Mr. Trudell said judges will often allow him or her to sit beside their lawyer if bail has been granted and there was no violence connected to the charge.

Putting the accused in the prisoner's dock is for those who were denied bail and is often a matter of court security.

Mr. Trudell pointed out that dangerous accused will have their shackles and handcuffs removed before the jury is brought in.

On the matter of what the prisoner wears in the courtroom, Mr. Trudell gets exercised.

"You didn't want the accused in jailhouse orange," he told me.

"You want the accused as beige as possible. Appearance is 40 per cent of perception everywhere and you don't want your client being forced to look like he's ready for death row.

"Juries should not draw any conclusions on the basis of appearance."

Judges will often allow accused to change into streetwear before being taken into court.

Maybe there are enough safeguards. But to be on the safe side why not let all people accused of crimes sit beside their lawyer, wearing what they want, without chains or handcuffs.

The golden thread is too easy to snap.