HM Inspectorate of Constabulary said that the force would now face an “enhanced level of monitoring” by inspectors as it attempted to turn around its performance.
It said that the force did not answer, or respond to, emergency or non-emergency calls within adequate timeframes, and too many calls were abandoned.
Identification of repeat and vulnerable callers was missed, and callers were not always given the appropriate advice on the preservation of evidence or crime prevention, the inspectorate found.
It also revealed that the force was unable to adequately manage registered sexual and violent offenders, which it said meant that an increasing risk of further offending may not be identified.
One in six forces in need of improvement
Devon and Cornwall followed the Metropolitan Police, Greater Manchester Police, Cleveland Police, Gloucestershire Constabulary, Staffordshire Police and Wiltshire Police into special measures. It means that one in six of the 43 forces in England and Wales are now judged to be in need of improvement.
Jim Colwell, the temporary Chief Constable of Devon and Cornwall Police, said: “We fully accept the findings of the HMICFRS inspection. I understand that these findings may cause concern in our communities and we are committed to delivering improvements.
“We have already commenced action in all three of these areas following the inspectorate’s initial inspection in January.”
Wendy Williams, the inspector of constabulary, said: “We move police forces into our enhanced level of monitoring, known as Engage, when a force is not responding to our concerns, or if it is not managing, mitigating or eradicating these concerns. The Engage process provides additional scrutiny and support.
“Devon and Cornwall Police has been asked to urgently produce an improvement plan and will meet regularly with our inspectors. We will work closely with the force to monitor its progress against these important and necessary changes.”
More details on the concerns which prompted the decision will be published in an inspection report next year.