The number of allegations proven against Sussex Police in the past year was well above the national average, according to new figures.
The Police Complaints Authority (PCA) said almost 22% of the allegations against the force by the public were supported.
The percentage represents a total of 371 individual complaints made against Sussex Police, of which 81 were upheld.
The figure compares badly to a national average of just over 15%.
In neighbouring Surrey, 27 allegations against the police were substantiated of 151 made, representing 18% upheld.
'Significant and unprecedented'
In a report released on Tuesday, the Police Complaints Authority confirmed it had supported a record percentage of complaints nationally.
Overall, one in six individual complaints led to misconduct action, up by 1.6% on the year before.
The number of officers against whom action was taken as a result, or wider procedures changed, also rose by 2% nationally.
PCA chairman Ian Bynoe said: "The rising rate of disciplinary action is significant and unprecedented.
"It is likely to result from higher standards of investigation, the lowering of the standard of proof from the criminal to the civil standard for hearings and a better resourced and trained PCA."