The commission would not be concerned by the results if the public showed more confidence in the complaints system, or improved access to it, IPCC Chair Dame Anne Owers said.
"In a recent survey commissioned by the IPCC, 38% of those surveyed did not have confidence in the fairness of the police complaints system, and that was even higher among young people," she said in a statement.
Most of complaints, 7,115, concerned London Metropolitan police. Northern England's Northumbria police saw complaints nearly double from 401 in 2012/13 to 794 in 2013/14, representing the largest percentage increase.
The report also revealed that the willingness of British citizens to register complaints about police officer conduct has surged from 68 percent in 2011 to 73 percent in 2014.
Owers added that the statistics show the complaints system is "complex, bureaucratic and over-focused on blame," and welcomed moves by government for reform.
In July 2014, UK Home Secretary Theresa May announced plans to boost public confidence in the police and improve standards of police integrity. On December 11, 2014, the Home Office sought opinions on reform of the police complaints system. The deadline for reform measure submissions is February 5, 2015.