Police watchdogs have criticised Lancashire Constabulary for the number of unrecorded crimes.
The force failed to record 20,000 crimes in a year, Her Majesty's Inspectorate of Constabulary and Fire and Rescue Services has estimated.
The watchdog rated the force as "inadequate" for the way it records reported crimes, in its latest inspection report, published in November 2017.
While the inspectors said Lancashire Constabulary had improved its recording methods, inspectors estimated that 16 per cent of crimes which were reported to officers, 20,000 incidents, failed to be recorded.
These included reports of rape, domestic abuse and violent crime.
The report said officers and staff too often failed to make correct crime recording decisions at the first opportunity.
“This is due to deficiencies in the constabulary's crime recording processes, insufficient understanding of crime recording requirements and limited supervision,” it said.
“The constabulary is failing to ensure it properly records all reports of rape, other sexual offences and violence, including domestic abuse crimes and crimes reported directly to its public protection department.
“Delays to the recording of a reported crime are leading to delays in the referral of victims to the constabulary's victim support service.”
READ MORE: Few crimes are being prosecuted in Lancashire
HMICFRS found that 84 per cent of violent crimes reported were recorded, leaving 20,000 reported crimes unrecorded. The inspection also stated 78 per cent of reported sex offences were recorded, with 8,500 incidents unrecorded.
The watchdog audited 1,438 crime reports between October and March 2016.
Among findings inspectors concluded 10 of 124 audited rape reports were misclassified or unrecorded.
However, they rated the force as "good" regarding the leadership and culture required to improve crime recording.
The report said: "We found that crime recording expectations had been publicised to officers and staff by senior leaders. Messages to officers and staff were clear and unambiguous."
Chief Constable Bill Skelly, National Police Chiefs' Council lead for crime recording, said: "Understanding crime in our communities is a core task of policing.
"It helps inform prevention activity and the identification of victims, witnesses and offenders and the services that forces and partners have in place."
Mr Skelly explained that police recording is one of many sources which forces use to develop an understanding of crime in their area.
"The NPCC continues to work closely with HMICFRS, the Home Office and forces to provide guidance to officers and staff on a proportionate application of the counting rules."