Devon and Cornwall Police has been ordered to make immediate improvements after a watchdog found it had an "inconsistent" response to child sexual exploitation.

Her Majesty's Inspectorate of Constabulary (HMIC) said its inspectors found the force's officers had a "lack of understanding" about the extent of the issue.

In some cases children were reported missing from home more than 10 times without any action taken, while in nine out of 10 of those cases inspectors found children could have been at risk of sexual exploitation.

"Officers did not always recognise that children who regularly go missing from home may be at risk of being groomed for sexual abuse," the report said.

While the force provided training to all officers and staff, not all had a "thorough awareness" of how to identify children at risk.

In one example, the case of a 13-year-old girl who sent more than 30 explicit images to an older man over the internet was closed without a suspect being identified or a referral to child social care services.

Another case involved the alleged sexual assault of a 15-year-old girl by her friend's father. While she was spoken to within two weeks, the suspect had not been arrested six months later and officers did not consider the "wider risk" he could pose.

The force responded well in the first instance to a report and in investigating it further, but recording of information was "frequently poor" and long-term strategies for safeguarding were "often absent".

HM Inspector of Constabulary Wendy Williams said the force showed "strong commitment to improving services" but although there were "examples of good work to protect children," it was not consistent.

She said: "We were concerned to find that in a significant number of cases we looked at, poor supervision and record keeping had undermined decision making and safeguarding measures. Some serious cases were investigated by non-specialist officers, resulting in delays, and potential risks posed by alleged offenders not being considered."

While the force is steps to address this how it tackles child exploitation, she said it must do "much more" to demonstrate that it can identify and safeguard children at risk.

"The response to children who regularly go missing from home also requires improvement, with a particular focus on early intervention and ensuring that officers and staff understand the link between children who regularly go missing and the risk of sexual exploitation. "

Detective Superintendent Paul Northcott, head of Devon and Cornwall's public protection unit, said the force has dedicated staff, trained in child abuse investigations, working daily to protect some of the most vulnerable people, with additional training including frontline staff to be implemented by the end of the year.

He said: "We recognise that we have to continue to improve the services we deliver and we have embraced a considerable amount of change already in response to this report."

Det Supt Northcott said the force was "working hard" to deliver improved outcomes for children and had to improve recording standards, as work was often not captured on its IT systems.

After the issue was flagged by Assistant Chief Constable Paul Netherton last November, the Home Secretary Theresa May announced that teenagers with mental health conditions would no longer be held in police cells.

The report found three cases of children being detained in cells in the 12 months prior to the inspection, down from previously, and Det Supt Northcott said: "The force also recognises the importance of not detaining children and young people in custody," particularly those with a mental illness.

The force has six weeks to respond to the report.