Almost two-thirds of appeals to the police watchdog over ignored complaints were upheld last year, figures have shown.
Forces "urgently need to examine their own practice to ensure that they are not blocking access to the complaints system", the Independent Police Complaints Commission (IPCC) said.
Some 1,374 appeals over a force's decision not to even record a complaint were made, up 16% from 2010/11, and almost two-thirds (61%) of these were upheld, with the watchdog telling forces to look at the complaints again.
Eight forces were told to reconsider complaints in three-quarters or more of appeals.
Overall, 6,339 appeals were made over complaints to police in 2011/12, up 3% from the previous year, with 38% of these upheld, up from 30% or less in the three preceding years.
In two forces, Northumbria and North Wales, more than half of appeals over complaints were upheld by the watchdog.
But the IPCC warned there was a wide variation between areas, with three forces upholding more than one in five complaints and seven upholding fewer than one in 10.
It also "still takes too long to resolve many complaints", IPCC chairwoman Dame Anne Owers said.
"It is of concern that not only has there been an increase in the number of appeals to the IPCC from those dissatisfied with the way their complaint was handled, there has also been a considerable increase in the proportion of appeals that we uphold," she said.
The report's findings "suggest that complainants are facing barriers to accessing the complaints system when they had a valid complaint, and that too many investigations are failing to achieve resolution for the complainant first time".