One in five solicitors advising suspects at police stations believe the chances of miscarriages of justice have "increased a lot" with the abolition of the unconditional right to silence, according to a poll commissioned by The Lawyer.
And while more than half of the 204 solicitors polled believe the danger of miscarriages of justice have increased to some degree, a clear majority believe the new law will make no difference to the conviction rate of the guilty.
The Law Society has seized on the poll as the first hard evidence that its opposition to the law change was justified.
The telephone survey of solicitors practising in England and Wales was designed to give an insight into how lawyers are coping with the change in the law which came into force in April.
Among key findings is a majority view that clients do not understand the new caution and overwhelming agreement that the pressure on suspects not to remain silent has increased.
The majority of the solicitors polled by The Lawyer said they were now a "little more likely" to advise their clients not to remain silent but a significant minority - 22 per cent - said it would make no difference.
The new law has barred police station advisers from counselling silence as a safety first option while boosting their need for better police pre-interview disclosure so they can advise their clients properly.
In the poll, six out of 10 advisers said advice was now "far more important than before" and a majority - 56 per cent - believed their workload had increased since the change. This reinforces earlier predictions of a legal aid budget increase.
While 66 per cent said the quality of pre-interview disclosure had improved, the rest said it had remained unchanged or had even got worse.
Roger Ede, secretary of the Law Society's criminal law committee, said Chancery Lane's opposition to the new law had been vindicated by the poll. He pointed with concern to the finding that 60 per cent of advisers believed the majority of their clients were unable to understand the caution.
"Our view is that the new law is too complex. It is worrying if members of the public don't understand a law which directly affects their chances of being put behind bars."
A Bar spokeswoman said its fears that miscarriages of justice would rise under the law were backed up by the survey.
Michael Burdett, of the London Criminal Courts Solicitors Association, and forensic psychologist Dr Eric Shepherd, who has published research indicating the caution is likely to be seen as a threat by the public, were both concerned at the number of lawyers who had seen no change in the quality of police disclosure.
Lyn Devonald, of the Legal Aid Practitioners Group, said: "In terms of achieving what it set out to do it doesn't appear that the new law has been a success."