Guidance to help prosecution witnesses prepare for trial may ‘damage’ conviction prospects and ‘reduce the efficient use of court time’, the Criminal Bar Association (CBA) has warned.

National rollout of the new Crown Prosecution Service (CPS) procedure, under which prosecution barristers must explain the court process to witnesses, started on 27 June.

It follows testing in Sheffield, Ipswich, Liverpool and Teeside, which the CPS said had ‘gone well’, with 89.5% of witnesses saying they were satisfied or fairly satisfied with the support they received.

The document, Speaking to witnesses at court: CPS guidance, set out the role played by prosecutors to ensure witnesses ‘give their best evidence’.

Prosecutors must meet all witnesses before they give evidence and explain the court procedure, the purpose of giving evidence and cross examination and the general nature of the defence case.

They must not ‘provide the detail of, discuss or speculate’ on specific questions a witness may face or discuss with them how to answer the questions. The guidance stresses that crown court advocates must carry out such conversations with a member of CPS staff present.

CBA chair, Mark Fenhalls QC, said that while ‘much of the guidance is sensible and appropriate’, he had ‘significant reservations’ about parts that ‘may damage the prospects of securing convictions’ and ‘actively reduce the efficient use of court time’.

‘For better or worse,’ he said, the guidance is part of barristers’ instructions, and warned them to ‘approach it with caution’ and report problems to the CBA.