The Crown Prosecution Service (CPS) in Berkshire and Buckinghamshire has been criticised for the way it handled sample cases in 2013.
Her Majesty's Crown Prosecution Service Inspectorate found examples of CPS Thames Valley prosecutors continuing cases which should not have been charged and problems processing cases efficiently before trial.
The inspection analysed the causes for its record of poor legal decisions, weak case progression and low rate of successful outcomes.
The report also noted that the area has worked to improve case listing arrangements in the magistrates' court in the past 18 months and the processing of Crown Court casework has improved more recently.
The new Chief Crown Prosecutor for CPS Thames and Chiltern, Adrian Foster said: "We acknowledge the recommendations made and are determined to bring about positive change, working closely with our police colleagues and others in the criminal justice service.
"We are committed to providing a high quality prosecution service to the communities we serve.
"We are determined to improve our performance and enhancements and adjustments have been and will continue to be made to address the issues raised in the report."
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