A newly published guide is aiming to help solicitors practise so-called “active defence” in the face of new restrictions imposed by the Criminal Procedures and Investigations Act.

The Act comes into force this week, despite a vociferous campaign by lawyers against its introduction. Under its provisions, it will be the responsibility of the police to decide what information should be disclosed to defence solicitors in criminal trials, including facts about the weakness of the police investigation.

The Law Society is marking the arrival of the Act with the launch of a book, Active Defence, and a press conference attended by, among others, Jim Nichol, the solicitor for the Bridgewater Three.

The book is written by forensic psychologist Dr Eric Shepherd – who first cast doubt on the reliability of the written confession in the Bridgewater Three case – and the society's criminal law committee secretary Roger Ede.

It sets out to show solicitors how to practise active defence, by systematically taking the prosecution case apart to expose its weaknesses and investigating the case for the defence.

Ede said the new law swept away all the judge-made law in relation to disclosure and put defence lawyers in a very difficult position.

“We're saying you can't realistically expect a police officer who wants to achieve a conviction to then set about taking that case apart by looking for material which undermines it.”

He said the Law Society had campaigned vigorously against the new Act. “We said there was a danger that miscarriages of justice would continue but at the same time they would never be discovered because the information prepared by solicitors to uncover that miscarriage may not be obtainable.”