When asked whether prison was an effective means of preventing crime, 57 per cent of the 300 randomly selected people questioned believed it was either 'very effective' or 'effective'. After a weekend of debate and discussion with experts and politicians, the figure dropped to 38 per cent.
Similar drops were seen in support for stiffer sentences and whether courts should send fewer people to prison.
The deliberative poll, conducted jointly by the Independent and Channel 4, was the first event of its kind to have taken place.
Three hundred people were questioned on their views before spending a weekend in Manchester debating the issues and discussing them with experts. At the end, they were questioned again.
The survey also disclosed strong opposition to the Government's planned abolition of the right of suspects to remain silent in police
interviews without it being held against them in court. Those supporting silence being held against an accused in court dropped from 57 per cent to 41 per cent between the two surveys.
The detailed results of the before and after surveys also show a marked drop in backing for the most popular means of preventing crime, such as more police on the beat and neighbourhood watch.
However, a majority still showed support for making prisons tougher and for the return of the death penalty - backing for which increased between the surveys.
Deliberative polling is the brainchild of Professor James Fishkin, professor of government at the University of Austin, Texas, and aims to create a survey of opinion that penetrates far deeper than conventional opinion polls.
A two-hour Granada Television programme recording the events of the weekend, Power and the People, was shown last night on Channel 4.
What the country really thinks, pages 8, 9
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