Juries should be split into three groups of four to allow every member an equal chance to participate, a new study has suggested.

Researchers from the psychology department at the University of Portsmouth found that in large groups, many people feel intimidated to speak out and barely contribute to the discussion.

Psychologists ran experiments by setting up two mock ‘juries’, sending one into a large room en masse and dividing up the second into smaller groups.

In the separated groups, participants were more likely to make their voice heard and did not feel overshadowed or bullied by dominant members of the panel.

Dr Bridget Waller, lead author of the research, said the results showed that a group of 12 is an artificially large conversational group that forces too many people into silence.

But the process worked much better if the dozen were split up and their thoughts later filtered into a large group discussion.

‘People naturally split into groups of four during conversations and so asking groups of 12 – such as juries – to make decisions is unlikely to result in all the people being able or willing to contribute to the decision-making process.

‘This is counter to scientific research which proves the more information is shared, the better the decisions will be.

‘In our experiments we found that jurors experienced greater shared information when they had the opportunity to talk in small groups, which is the basis of any good decision.’

Every year nearly 400,000 people in Britain serve as jurors, with previous research suggesting that up to a third do not actively take part during deliberations and up to a quarter remain completely silent during discussions.