Devon and Cornwall Police have been ordered to make immediate improvements after inspectors found almost one-in-five-crimes were going unrecorded.
The force was put on notice by Her Majesty's Inspectorate of Constabulary (HMIC) in May when an interim report showed the force should have recorded 113 offences compared to the 94 it did.
HMIC has now published its full report, including a raft of recommendations, which revealed broadly similar results.
Devon and Cornwall Police should have formally classified 117 crimes, compared to the 98 which were, according to a dip sample carried out by inspectors.
They also found fault with the force's recording of "no crimes" – where officers judged no offence has actually taken place. Out of, 104 no-crime records, 10 were found to be inaccurate, including eight cases of robbery.
In all, HMIC made eight recommendations, around training, computer systems and processes, three of which need to be carried out immediately.
Deputy Chief Constable Bill Skelly said it was "clear" there were "some areas we must address" but that the reported also highlighted "areas of good performance".
"The report identifies that Devon and Cornwall Police has robust leadership and a sound culture in the way crime is recorded in Devon and Cornwall," he said. "We do not deliberately over or under crime – which is what we fully expected HMIC to find.
"It is important to make the point that this report looked at our processes, not how we treat victims or actually investigate crime – this was about the way crime is recorded.
"It is hugely important that people in Devon and Cornwall have confidence in the way we record crime and this report acknowledges that we have ethical and victim-centred processes in place.
"Of the recommendations raised by HMIC, such as some cases not being crimed but were recorded as an incident, we have already changed some of our processes as a result of initial feedback received, and are in the process of dealing with the others.
"While this has not changed the actual investigation process and service to the victim, we recognise this is a more transparent approach and this can assist in building public confidence."
Mr Skelly said crime figures were "only one measure of performance" saying public confidence in the force and satisfaction levels among victims and witnesses were "equally relevant measures".
He added: "Modern policing is all about providing the best service possible with the resources available and learning is a critical part of progress. There will always be lessons to be learnt, that's how we improve and HMIC has a valuable role to play in that process.
"I am confident that we record crime ethically and the public should gain confidence from that and we will continue to make positive changes to our processes in areas that have been identified for improvement."
The force was among 21 inspected by following long-standing concerns nationally that offences are not being recorded consistently.
When the interim results were announced, Home Secretary Theresa May said they exposed "unacceptable failings by the police" and warned the final figures may show a spike in recorded crime.
