More than one in three people do not think the police handle complaints fairly, a damning survey has revealed.
The poll for watchdog the Independent Police Complaints Commission (IPCC) found that 35% of adults and teenagers were not very or not at all confident that forces deal with complaints fairly.
One in five said they would be worried about police harassment if they made a complaint.
Ipsos Mori questioned 4,067 adults and teenagers aged 15 and over in February and March this year, and found that the number of people who are happy with their contact with the police has dropped to 2004 levels.
Satisfaction reached a peak in 2011, when three-quarters of those surveyed said they were happy, down to 66% this year. Those from ethnic minority groups continue to be less happy (56%) than white people (68%).
The research also revealed that 38% of those asked were not very or not at all confident that they would know how to complain about the police.
IPCC chairwoman Dame Anne Owers said: "The majority of the 30,000 complaints made annually about the police are handled by the police service itself.
"This survey shows that too many people are still either unsure of how to make a complaint about the police or don't believe their complaint will be dealt with fairly. It is particularly worrying that young people and those from ethnic minorities have lower confidence in the complaints system.
"There is clearly more work to be done by both the police and IPCC to improve access, awareness and trust in the complaints system and those who work in it."
More of the teenagers and adults surveyed had contact with the police in the previous 12 months than in recent years - 23% compared to 20% in 2011, but down from 27% or 28% in 2004 to 2009.
People from a minority ethnic background were less likely to have had contact with the police - 13% versus 26% of white people.
Minority ethnic groups were less happy with their police contact in 2014 than ten years earlier - 56% in 2014 compared to 61% in 2004; while white people were happier - 65% were happy in 2004 and 68% in 2014.