Six police officers involved in the stop and search of athlete Bianca Williams are being investigated for gross misconduct.
The Great Britain sprinter and her partner, Ricardo dos Santos, a Portuguese sprinter, were handcuffed in Maida Vale, west London, on 4 July last year.
Ms Williams said she had been racially profiled by police, who separated the couple from their infant son.
She told how she was “really scared” during the ordeal, which left her feeling “like we were the scum of their shoe”.
Police said they stopped a Mercedes driven by Mr dos Santos – while Ms Williams and their son were sitting in the back – due to the vehicle being driven “erratically”.
Almost a year to the day since the incident, police watchdog the IOPC said it is “in the final stages” of an investigation into the officers’ conduct.
Three officers are subject to a gross misconduct investigation for potential breaches of police standards of professional behaviour relating to equality and diversity.
The rules require officers to “act with fairness and impartiality and not to discriminate unlawfully or unfairly”.
The three were already being investigated for various breaches relating to use of force; duties and responsibilities; and authority, respect and courtesy.
The fresh investigation was launched after a “range of new evidence” was reviewed, an IOPC spokesperson told Sky News.
Two of the three officers are also being questioned over potential breaches relating to honesty and integrity.
Meanwhile, a fourth officer is being investigated for standards breaches linked to equality and diversity; and duties and responsibilities.
Two more have been quizzed over possible breaches regarding use of force; duties and responsibilities; and authority, respect and courtesy.
“All officers have now been interviewed,” the IOPC spokesman told Sky News.
“Our investigatory work has now concluded and preparation of the final report is underway.”
The Metropolitan Police said it “continues to fully co-operate with the IOPC investigation”.
“No officer is suspended or subject to restricted duties,” the force said in a statement.
Ms Williams and Mr Dos Santos were searched on suspicion of having drugs and weapons.
Metropolitan Police Dame Commissioner Cressida Dick apologised to Williams.
The force initially insisted no misconduct had taken place, having reviewed footage from multiple cameras.
But it referred itself to the IOPC after “significant public interest”.
Both athletes are preparing for the Tokyo Olympics.
Mr dos Santos told The Guardian: “Finally this looks like a more credible investigation now.
“Discrimination and a lack of honesty was at the heart of the officers’ behaviour that day and now at last, it is what they are actually being investigated for.”