Lawyer Kiran Daurka, who represents Howard, called the judgment "a damning indictment" of the police. She said police have failed to change discriminatory practices in the 15 years since the force was found to be "institutionally racist" by an official inquiry into its investigation of the notorious murder of black teenager Stephen Lawrence.
Police investigators looking into Howard's claims followed a policy of deleting all references to sex and race discrimination in their file, the tribunal found.
The only explanation for this policy was a desire to remove all written references to discrimination because tribunal proceedings could only be started in cases where discrimination was found, the tribunal said.
In a statement, police denied there is such a policy. The Metropolitan Police, also known as Scotland Yard, said in a statement it was disappointed by the tribunal's findings and would seek legal advice on the issue.
The tribunal also revealed evidence of two further cases, unconnected to Howard, where police had asked for mentions of discrimination to be removed from reports.
John Tully, chairman of the Metropolitan Police Federation that supported Howard's claim, said discrimination remains a serious problem.
"It is of concern that such issues are still prevalent in the Metropolitan Police service, despite the many measures introduced to address the problem," he said.