It is a pinnacle of the adversarial system of justice that governs criminal trials in this country, but most jurors asked to determine a person's fate struggle to understand what ''beyond reasonable doubt'' means.

A NSW Law Reform Commission review of the directions judges give to juries finds they are not working, are outdated, overly complex and need to be clearer.

Illustration: Cathy Wilcox

The review's report, seen by Fairfax Media, says this has resulted in unnecessarily prolonging already lengthy trials.

It finds that both its research and anecdotal evidence suggests jurors do not really understand the meaning of ''beyond reasonable doubt''.