A teenager was detained in police custody and went without food or water for 44 hours, a report has found.
HM Inspectorate of Constabulary (HMIC) found the 16-year-old girl went without eating or drinking for almost two days while she was detained under the Mental Health Act by Nottinghamshire Police, the BBC reports.
The force said the girl was offered food and drink on various occasions but refused both.
HMIC inspected Nottinghamshire Police's child protection work in September 2014 and found some children were being held in police custody overnight unnecessarily.
The report said: "The most serious case seen by inspectors involved a 16-year-old girl who was detained for 52 hours in the central police custody suite before being transferred to a healthcare setting.
"It was only after the girl had been in custody for 44 hours that custody staff realised that she had gone without food or water.
"She was subsequently treated by a paramedic before being taken to hospital."
It also discovered that there was a lack of awareness of child sexual exploitation in some areas of the force, although it stressed that staff in charge of child abuse investigations were committed, dedicated and discerning.
Zoë Billingham, from HMIC, said it is “essential” that the force take measures to ensure this does not happen again.
"It is clear that that despite good work in many areas, Nottinghamshire Police needs to do more to improve its approach to protecting children,” she said.
Nottinghamshire Police's Assistant Chief Constable, Steve Jupp, said: "We never want to be in a position where children need to be taken into custody, whether for crimes or because of mental health issues.
He said the force will continue to work with its partners to find “alternative accommodation” for children wherever it can.
"A full review of the case into the 16-year-old girl who was arrested has been conducted," he added.
"She was offered food and drink on several occasions while in custody but declined. Doctors and nurses assessed her welfare, and she was deemed to require specialist mental health assistance, and attempts were made over many hours to find appropriate accommodation."
A damning assessment in November found 263 children sectioned under the mental health act were held in police cells in 2013, often because there were no beds in hospital available.
Assistant Chief Constable Paul Netherton of Devon and Cornwall Police expressed concern in the same month that a 16-year-old girl was being held in police custody because there were no beds available in nearby hospitals.
He branded the situation as "unacceptable" and said custody on a Friday and Saturday night was “no place for a child suffering mental health issues” to be.Reuse content