The Metropolitan Police is failing to record more than 94,500 crimes every year, amounting to around 10.5% of the total reported to the force by the public.
When it came to violent crime 87.6% of incidents reported to police were recorded – and the watchdog highlighted domestic abuse as among the areas that were not being adequately registered.
Despite this, however, the country’s largest police force was rated “good” by Her Majesty’s inspector of constabulary.
Lincolnshire police, on the other hand, was found to be “heavily inadequate” by the watchdog.
Records between June and November 2017 estimated that around 9,400 crimes, 18.8% of the total reported to the force, went unrecorded.
Violent crimes were particularly neglected, with fewer than three quarters (72.7%) of incidents including sexual offences, grievous bodily harm, rape and domestic abuse recorded by police.
The report said this meant that “on too many occasions” the police force was failing victims of crime, and inspector of constabulary Zoe Billingham described the shortfall as “of very great concern”.
“The importance of correctly recording crime cannot be overlooked, or simply passed off as a bureaucratic measure,” she said.
“If a force does not correctly record crime it cannot properly understand the demand on its services, nor provide support to those who need it most.”
Humberside police force was also singled out as in need of improvement, with 79.4% of reported violent crime in the area being reported.
Overall Humberside police failed to record 14,200 crimes annually – amounting to 14.3% of the total reported.
Lincolnshire police deputy chief constable Craig Naylor said measures were being taken to improve reporting and said the standards upheld by the force “had not slipped”.
“We are deeply disappointed by this report and absolutely committed to ensuring we resolve the problem quickly and effectively,” he said.
“Our focus and commitment is to ensure victims are at the centre of all that we do and I am confident that, despite issues in how we have recorded some crimes, that service has not slipped from the high standards we set ourselves.”