One in four incidents written off by some police forces last year should have been recorded as crimes, say inspectors.
While some forces recorded all crimes correctly, others only got the decision right three-quarters of the time, meaning hundreds of crimes were not investigated, Her Majesty's Inspectorate of Constabulary (HMIC) said.
Its review of the quality of police crime and incident reports found that, on average, 87% of "no crimes" were correctly reported last year, compared with 64% in 2009.
But there was a "wide variation" between forces, and systems and processes need to be improved, the inspectors said.
The review, which looked at almost 5,000 records from the 43 forces across England and Wales and British Transport Police, found 18 made correct decisions in 95% or more of the incidents checked, 15 in 90%-94% of cases and 11 in 86%-89% of cases.
Vic Towell, an assistant inspector, said: "The findings are indicative and provide assurance that the crime figures published by their police forces are being probed.
"Whilst the majority do well, the variation between the best and worst remains too wide and needs to improve."
The report also found that "no crime" decisions in cases involving violence were correct 84% of the time.
"Equally reassuring is the finding that 'no-crime' compliance for rape offences is higher than the average (90%), which indicates that forces are giving greater scrutiny to their most serious crimes," the report added.
"These results show that forces understand the importance of making correct no-crime decisions, particularly for the more serious crime types."
The inspectors found only a low number of crimes were recorded from anti-social behaviour cases and the identification of repeat, vulnerable and intimidated victims was "poor" at the first point of contact.
HMIC said further work was needed later this year as the inspectors only studied a small sample of cases.
Policing minister Nick Herbert said: "Recording crime properly is vital if the public are to have confidence in the police.
"We commissioned this report to shine a light on recording practices and there are issues in some forces which need to be addressed.
"We want people to have accurate and clear crime data so they can hold their local force to account and make sure the right action is being taken to drive down crime in their area."
He added that the "varied response" to anti-social behaviour was particularly concerning.
"We have been very clear that much of what is described as 'anti-social behaviour' is actually crime, and where this is the case forces should treat it as such, and give victims the service they deserve," he said.
Chief Constable Steve Finnigan, the lead on performance management for the Association of Chief Police Officers (Acpo), added: "The UK is regarded as having one of the most rigorous crime recording regimes in the world and it is encouraging that this review by HMIC demonstrates that national crime statistics are more robust than ever.
"Nevertheless, there is always scope for improvement and Acpo continues to lead work to strengthen the accuracy and consistency of recording decisions."