The IPCC said the criticisms of the three forces applied in particular to discrimination complaints brought by members of the public, which it said were "poorly handled from beginning to end".
Too many complaints about discrimination from the public were resolved locally - without a formal investigation - when it was not appropriate to do so, the report found.
The quality of the local resolutions was also poorer than that of formal investigations, it added.
Of 170 complaints from the public - out of 202 complaints in total examined by the IPCC alleging discrimination - 94 were investigated and, of those, no discrimination allegations were upheld, it said.
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