A report by the police watchdog has found Scotland Yard is failing in the way it handles complaints of racism and discrimination against officers, a decade after the force vowed to stamp out prejudice in the ranks.

The report by the Independent Police Complaints Commission (IPCC) led the Met to admit it was letting down the public in the way it handled racism complaints.

The report followed allegations of police racism, some of which were revealed by the Guardian.

Some 3% of complaints against the Metropolitan police, Britain's largest force, involve claims of racism. The IPCC said it was "crucial to public confidence" that racism complaints were handled fairly.

The IPCC commissioner Jennifer Izekor said: "This report shows that, though there are some examples of good practice, in general there is an unwillingness or inability to deal with these complaints robustly and effectively.

"Too often, complaints are dismissed without proper investigation or resolution, complainants are not properly engaged with, and lessons are not learned.

"In relation to race complaints, it can exacerbate a negative experience if the racial element is not properly addressed. It can also mean that officers are not held to account, or do not learn from their actions.

"We know that there is less confidence both in policing and in the complaints system among BME [black and minority ethnic] communities. If the Metropolitan police service is serious about building that confidence, there will need to be a cultural change to complaints handling."

The IPCC report said: "All too often the MPS's [Metropolitan police service's] handling of complaints alleging racism was not sufficiently robust, fair, or customer-focused."

The IPCC called for "a cultural change in the way the MPS deals with such complaints, supported by training, monitoring and community feedback".

The IPCC paid special attention to 20 cases where the Met was left to investigate racism cases itself. It found in the majority, 13 cases, "the investigating officer made no effort to obtain additional evidence that could have supported the allegation of racism".

In its response the Met vowed to reform and learn. The assistant commissioner Simon Byrne welcomed the report's critical findings and said: "It is powerful, showing the way we deal with complaints involving racism is letting down the public."

He added the force was determined to "be less defensive and accept when we are not performing as well as we should be".

Byrne said the force favoured an independent ethics panel to oversee misconduct proceedings for the Met police, and wanted senior officers to meet those who felt let down to humanise complainants and improve their negative experiences of complaining about police racism.